Hermann von Helmholtz and the Foundations of Nineteenth-Century Science 9780520914094

Table of contents :
Contents
Illustrations
Acknowledgments
Contributors
Abbreviations
Chronological Listing of the Principal Events and Publications of Helmholtz's Life and Career
Introduction: Helmholtz at the Borders of Science
Part One. Physiologist
1. Helmholtz and the German Medical Community
2. Experiment, Quantification, and Discovery: Helmholtz's Early Physiological Researches, 1843-50
3. The Eye as Mathematician: Clinical Practice, Instrumentation, and Helmholtz's Construction of an Empiricist Theory of Vision
4. Consensus and Controversy: Helmholtz on the Visual Perception of Space
5. Innovation through Synthesis: Helmholtz and Color Research
6. Sensation of Tone, Perception of Sound, and Empiricism: Helmholtz's Physiological Acoustics
Part Two. Physicist
7. Helmholtz's Ueber die Erhaltung der Kraft: The Emergence of a Theoretical Physicist
8. Electrodynamics in Context: Object States, Laboratory Practice, and Anti-Romanticism
9. Helmholtz's Instrumental Role in the Formation of Classical Electrodynamics
10. Between Physics and Chemistry: Helmholtz's Route to a Theory of Chemical Thermodynamics
11. Helmholtz's Mechanical Foundation of Thermodynamics
Part Three. Philosopher
12. Force, Law, and Experiment: The Evolution of Helmholtz's Philosophy of Science
13. Helmholtz's Empiricist Philosophy of Mathematics: Between Laws of Perception and Laws of Nature
14. Helmholtz and Classicism: The Science of Aesthetics and the Aesthetics of Science
15. Helmholtz and the Civilizing Power of Science
Bibliography
Index

Citation preview

Hermann von Helmholtz and the Foundations of NineteenthCentury Science

CALIFORNIA STUDIES IN THE HISTORY O F SCIENCE J.L. HEILBRON, Editor

The Galileo Affair: A Documentarj1 History, edited and translated by Maurice A. Finocchiaro The New World, 1939-1946 (A History of the United States Atomic Energy Commission, volume I), by Richard G. Hewlett and Oscar E. Anderson, Jr. Atomic Shield, 1947-1952 (A History of the United States Atomic Energy Commission, volume 2), by Richard G. Hewlett and Francis Duncan Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission (A History of the United States Atomic Energy Commission, volume 3), by Richard G. Hewlett and Jack M. Holl Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory, Volume 1, by J.L. Heilbron and Robert W. Seidel ScientiJic Growth: Essays on the Social Organization and Ethos of Science, by Joseph Ben-David, edited by Gad Freudenthal. Physics and Politics in Revolutionary Russia, by Paul R. Josephson From c-Numbers to q-Numbers: The Classical Analogy in the History of Quantum Theory, by Olivier Darrigol The Quiet Revolution: Hermann Kolbe and the Science of Organic Chemistry, by Alan J. Rocke Hermann von Helmholtz and the Foundations of Nineteenth-Century Science, edited by David Cahan

Hermann von Helmholtz and the Foundations of NineteenthCentury Science Edited by David Cahan

University of California Press Berkeley /

Los Angeles / London

University of California Press Berkeley and Los Angeles, California University of California Press London, England Copyright O 1993 by The Regents of the University of California Library of Congress Cataloging-in-Publication Data Hermann von Helmholtz and the foundations of nineteenth-century science / edited by David Cahan. p. cm. - (California studies in the history of science ; 12) Includes bibliographical references and index. lSBN 978-0-520-08334-9 (alk. paper) 1. Helmholtz, Hermann von, 1821-1894. 2. Science-History-19th century. 3. Scientists-Germany-Biography. 4. Physiolo~sts-Germany-Biography. I. Cahan, David. 11. Series. Q 143.H5H47 1994 509.2--dc20 [Bl 92-16285 CIP Printed in the United States of America

The paper used in this publication meets the minimum requirements of ANSVNISO Z39.48-1992 (R 1997)(Permanence o f Paper). @

"Ich bewundere den originellen, freien Kopf Helmh[oltz]. immer mehr." Albert Einstein, August 1899

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Contents

Illustrations xi .. . Acknowledgments x111 Contributors xv Abbreviations xix Chronological Listing of the Principal Events and Publications of Helmholtz's Life and Career xxi

Introduction: Helmholtz at the Borders of Science, David Cahatz 1 Part One

Physiologist 1 Helmholtz and the German Medical Community,

Arleen Tuchman

17

2 Experiment, Quantification, and Discovery: Helmholtz's Early Physiological Researches, 1843-50, Kathryn M. Olesko and Frederic L. Holmes 50 3 The Eye as Mathematician: Clinical Practice, Instrumentation, and Helmholtz's Construction of an Empiricist Theory of Vision, Timothy Lenoir 109

viii

Contents

4 Consensus and Controversy: Helmholtz on the Visual Perception of Space, R. Steven Turner 154

5 Innovation through Synthesis: Helmholtz and Color Research, Richard L. Kremer 205 6 Sensation of Tone, Perception of Sound, and Empiricism: Helmholtz's Physiological Acoustics,

Stephan Vogel Part Two

259

Physicist

7 Helmholtz's Ueber die Erhaltung der Krafi The Emergence of a Theoretical Physicist, Fabio Bevilacqua 29 1

8 Electrodynamics in Context: Object States, Laboratory Practice, and Anti-Romanticism, Jed Z. Buchwald 334 9 Helmholtz's Instrumental Role in the Formation of Classical Electrodynamics, Walter Kaiser 374

10 Between Physics and Chemistry: Helmholtz's Route to a Theory of Chemical Thermodynamics, Helge Kragh 403 11 Helmholtz's Mechanical Foundation of Thermodynamics, Gunter Bierhalter 432

Part Three

Philosopher

12 Force, Law, and Experiment: The Evolution of Helmholtz's Philosophy of Science, Michael Heidelberger 46 1 13 Helmholtz's Empiricist Philosophy of Mathematics: Between Laws of Perception and Laws of Nature, Robert DiSalle 498

Contents

14 Helmholtz and Classicism: The Science of Aesthetics and the Aesthetics of Science, Gary Hatfield 522 15 Helmholtz and the Civilizing Power of Science, David Cahan 559 Bibliography Index 637

603

ix

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Illustrations

Figure 1. I. Schematic drawing of the path taken by light as it travels through the ophthalmoscope. Figure 2.1. Helmholtz's data for alcohol, water, and spiritous extracts from a muscle. Figure 2.2. Weber's apparatus for studying the contraction of a muscle. Figure 2.3. Helmholtz's muscle curve. Figure 2.4. Helmholtz's apparatus for measuring the time course of muscle contraction and the propagation velocity of the nerve impulse. Figure 2.5. Helmholtz's nerve propagation velocity data from 6 January 1850 with the results of least-squares calculations. Figure 2.6. Helmholtz's graphical representation of data on the behavior of a stimulated muscle when no overload was applied. Figure 2.7. Helmholtz's graphical representation of data on the effect of three degrees of muscle fatigue on the muscle's ability to lift a weight. Figure 3.1. Wundt's ophthalmotrope. Figure 3.2. Primary axes of rotation and Listing's Plane. Figure 3.3. Motion around axes in Listing's Plane. Figure 3.4. Projection of direction lines and objective verticals in the visual field.

xii

Illustrations

Figure 3.5. Eye motion according to the Principle of Easiest Orientation. Figure 4.1. Stereogram by Charles Wheatstone, purporting to refute the theory of identity. Figure 4.2. Pattern of corresponding retinal meridians, eyes in the primary position. Figure 4.3. Demonstration by Helmholtz that the horopter is the region in which the perception of relief is most acute (1863). Figure 4.4. Afterimage experiment by Helmholtz confirming Listing's law of eye movements (1 863). Figure 4.5. Experimental test by Helmholtz of Hering's theory of retinal depth values. Figure 4.6. The compensating rotation of the core plane, induced by the closing of one eye, according to Hering. Figure 4.7. Experiment by Helmholtz, purporting to refute Hering's core-plane rotation (1 867). Figure 5.1. Brewster's absorption experiments (1823). Figure 5.2. Brewster's triple spectrum ( 183 1). Figure 5.3. Helmholtz's absorption experiments (1852). Figure 5.4. Helmholtz's "V-slit" mixed spectra (1852). Figure 5.5. Helmholtz's revised mixing experiments (1855). Figure 5.6. Helmholtz's barycentric curve for color mixing (1855). Figure 5.7. Helmholtz's hypothetical response curves for Young's receptors (1860). Figure 8.1. Herwig's apparatus for use in refuting Helmholtz's potential. Figure 8.2a. Hertz's original diagram of a Wheatstone bridge with double-wound spiral inductors. Figure 8.2b. A modern rendering of Hertz's original diagram. Figure 8.3. A modern rendering of Hertz's apparatus with a floor circuit in place of a spiral inductor.

Acknowledgments

In the course of preparing this volume the University of Chicago generously agreed to sponsor a two-day conference (October 1990) on "Hermann von Helmholtz: Scientist and Philosopher." Most of the contributors to this volume were able to attend the conference, which gave us an excellent opportunity to discuss one another's papers and views on Helmholtz, and to explore some of the broader themes of his work. I want in particular to thank three individuals at Chicago for making the conference possible: George Stocking, Director of the Morris Fishbein Center for the Study of the History of Science and Medicine; Robert J. Richards, Chairman of the Committee on the Conceptual Foundations of Science; and Patricia Swanson of The John Crerar Library, which provided us with an ideal setting for stimulating discussion. It is a great pleasure to acknowledge Chicago's gracious support. It is an equally great pleasure to acknowledge the help of three colleagues who acted as outside commentators on the final versions of the three Parts of this volume: John E. Lesch (Berkeley), who commented on the essays constituting Part One (Helmholtz as physiologist); Ole Knudsen (Aarhus), who commented on Part Two (Helmholtz as physicist); and Mitchell G. Ash (Iowa), who commented on Part Three (Helmholtz as philosopher). To all three I owe thanks for their extensive comments and judicious criticisms.

xiv

Acknowledgments

Finally, I owe general thanks to Richard L. Kremer and R. Steven Turner, two of my fellow contributors to this volume, for their counsel on numerous points concerning Helmholtz; and to Elizabeth Knoll, my sponsoring editor at the University of California Press, for her faith in this project and her patience in awaiting its completion. -David Cahan

Contributors

Fabio Bevilacqua is Associate Professor of the History of Physics in the Department of Physics "A. Volta" at the University of Pavia. He has published articles on the history of nineteenth-century physics and on the use of the history of science in science education, as well as a book entitled The Principle of Conservation of Energy and the History of Classical Electromagnetic Theory (Pavia: LaGoliardica Pavese, 1983). Giinter Bierhalter, an independent scholar living in Pfonheim, in the Federal Republic of Germany, is the author of articles on nineteenth-century thermodynamics, including attempts to establish the mechanical foundations of thermodynamics and the problem of irreversibility. His principal scholarly interests are the history of the foundations of mechanics, extremum principles in physics, thermodynamics, and quantum physics. He is currently working on the history of nineteenth-century electrodynamics. Jed 2. Buchwald is Bern Dibner Professor of the History of Science at the Massachusetts Institute of Technology and Director of the Dibner Institute for the History of Science and Technology. In addition to numerous articles on the history of nineteenth-century electromagnetism and optics, he is also the author of two book-length studies: From Maxwell to Microphysics. Aspects of Electromagnetic Theory in the Last Quarter of the Nineteenth Century (Chicago and London: The University of Chicago Press, 1985), and The Rise of the Wave Theory

xvi

Contributors

of Light. Optical Theory and Experiment in the Early Nineteenth Century (Chicago and London: The University of Chicago Press, 1989). He has recently completed a book entitled The Creation of Scientijic Efects: Heinrich Hertz and Electric Waves (forthcoming). David Cahan is Associate Professor of History at the University of Nebraska-Lincoln. His research concerns the history of physics and the social history of science from the early Enlightenment to the present. He has published articles on physics in nineteenth- and early twentieth-century Germany; has written a book entitled An Institute for an Empire: The Physikalisch-Technische Reichsanstalt, 1871-1918 (Cambridge, New York, New Rochelle: Cambridge University Press, 1989);and has edited Letters ofHermann von Helmholtz to His Parents: The Medical Education of a German Scientist, 1837-1846 (Stuttgart: Franz Steiner Verlag, 1993). Robert DiSalle is Assistant Professor of Philosophy at the University of Western Ontario. His research concerns the history and philosophy of science, especially historical and philosophical issues connected with the foundations of mechanics and the development of general relativity. He is currently working on a critical account of space-time principles in the history of physics. Gary Hatjield is Professor of Philosophy at the University of Pennsylvania, where he is also a member of the Graduate Group in History and Sociology of Science. He is the author of numerous articles in the history of philosophy and science and in the philosophy of psychology, as well as a book entitled The Natural and the Normative: Theories of Spatial Perception from Kant to Helmholtz (Cambridge, Mass.: MIT Press, 1990). He is currently researching the development of the distinction between Naturwissenschaften and Geisteswissenschaften by Helmholtz and his neo-Kantian contemporaries. Michael Heidelberger teaches philosophy at the University of Freiburg, in the Federal Republic of Germany. He is the co-author of Natur und Erfahrung, 2nd ed. (Reinbek bei Hamburg: Rowohlt, 1985), a study of the Scientific Revolution; and the co-editor of and a contributor to The Probabilistic Revolution, vol. 1: Ideas in History (Cambridge, Mass.: MIT Press, 1987). He has published numerous articles in the history and philosophy of science, and has recently published a book entitled Die innere Seite der Natur: Gustav Theodor Fechners wissenschaftlich-philosophischeWeltauffassung (Frankfurt am Main: Klostermann, 1993). Frederic L. Holmes is Avalon Professor and Chairman of the Section of the History of Medicine in the Yale University School of Medicine. He is the author of several books and numerous articles in the history of chemistry and the life sciences in the eighteenth and nineteenth

Contributors

xvii

centuries. Most recently he has written Hans Krebs: The Formation qf a ScientiJic Llfe (Oxford: Oxford University Press, 1991) and Bet ween Biology and Medicine: The Formation of Intermediary Metabolism (Office for History of Science and Technology [Berkeley], 1991). He is presently working on Justus von Liebig and early nineteenth-century German chemistry; on topics in the early years of molecular biology; and, with Kathryn M. Olesko, on Hermann von Helmholtz's early scientific career, from which their essay in this volume is drawn. Walter Kaiser holds the Lehrstuhl for the History of Technology at the Rheinisch-Westglische Technische Hochschule Aachen. He has written articles on the history of electrodynamics and solid state physics, and, more generally, in the history and philosophy of science and the history of technology. He is the author of Theorien der Elektrodynamik i m 19. Jahrhundert (Hildesheim: Gerstenberg Verlag, 1981); has edited Ludwig Boltzmann's Vorlesungen uber Maxwells Theorie der Elektricitat und des Lichtes (Graz: Akademische Druck- und Verlagsanstalt, 1982); and has co-authored the Propylaen Technikgeschichte, vol. 5 1914-1 990 (Berlin: Propylaen Verlag, 1992). Helge Kragh is a researcher at the Roskilde University Centre in Denmark, where he works with a project on the history of technology and culture in Denmark since 1750. He was associate professor of physics and history at Cornell University from 1987 to 1989, and has written articles and books on the history of modern physical science. His most recent publications include An Introduction to the Historiography of Science (Cambridge, London, and New York: Cambridge University Press, 1987), and Dirac: A ScientiJic Biography (Cambridge, New York, and Port Chester: Cambridge University Press, 1990). Richard L. Kremer is Assistant Professor of History at Dartmouth College. He has edited Letters ofHermann von Helmholtz to His Wife, 1847-1859 (Stuttgart: Franz Steiner, 1990), and is completing a booklength monograph on the "culture of experiment" in physiology at German universities between 1800 and 1865. Timothy Lenoir is Associate Professor of History and of History of Science in the Program in History of Science at Stanford University. He has published numerous articles on the history of the life sciences in the nineteenth century as well as a book: The Strategy of Lzfe: Teleology and Mechanics in Nineteenth-Centurv German Biology (Dordrecht and Boston: D. Reidel, 1982; paperback reprint: Chicago and London: The University of Chicago Press, 1989). Kathryn M. Olesko is Associate Professor of History at Georgetown University. She is the author of Physics as a Calling: Discipline and Practice in the Konigsherg Seminar .for Physics (Ithaca and London: Cornell University Press, 1991 ) and the editor of Science in Germany:

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Contributors

Problems at the Intersection of Intellectual and Institutional History (Osiris 5 [1989]). She is currently writing a book entitled The Meaning of Precision, which examines the scientific, political, economic, and cultural meaning of precision measurement in Germany from 1780 to 1870. With Frederic L. Holmes she is preparing a monograph on Hermann von Helmholtz's early scientific career, from which their essay in this volume is drawn. Arleen Tuchman is Assistant Professor of History at Vanderbilt University, where she teaches the history of science and medicine. She has published several articles on the rise of scientific medicine in nineteenth-century Germany, as well as a book entitled Science, Medicine, and the State in Germany: The Case o f Baden, 1815-1871 (Oxford and New York: Oxford University Press, 1993). Her current project is tentatively entitled Gender and Scientific Medicine at a Crossroad: The Life and Times of Marie Zakrzewska, 1829-1902, a biographical study of a German midwife who became one of the most prominent female physicians in nineteenth-century America. R. Steven Turner teaches the history of science and technology at the University of New Brunswick in Fredericton, N.B., Canada. He has published widely on the development of the German university system in the eighteenth and nineteenth centuries; the history of sensory physiology and psychology in the nineteenth century; and the career and work of Hermann von Helmholtz. Stephan Vogel is a research fellow in the Department of Linguistic Information Processing at the University of Cologne, in the Federal Republic of Germany. He is currently completing his Ph.D. degree in History and Philosophy of Science at Cambridge University with a thesis on the history of nineteenth-century acoustics.

Abbreviations

Note: Unless otherwise noted, all journal articles and books cited in this volume are by Hermann (von) Helmholtz. Most of Helmholtz's scientific articles were reprinted in his Wissenschaftliche Abhandlungen and are cited in this volume simply as "in WA." The following abbreviations are used in both the Notes and the Bibliography:

BJHS DSB

Handbuch Handbuch2

HSPS

Archiv fur Opthalmologie. Annalen der Physik (und Chemie]. Akademie der Wissenschaften, Berlin, Archiv, Signatur: Helmholtz NachlaB. British Journal for the History o f Science Dictionary of Scientijc Biography. Ed. Charles Coulston Gillispie. 16 vols. New York: Charles Scribner's Sons, 1970- 1980. Hermann von Helmholtz. Handbuch der physiologischen Optik. Leipzig: Leopold Voss, 1856-67. Hermann von Helmholtz. Handbuch der physiologischen Optik. 2nd rev. ed. Ed. Arthur Konig. Hamburg and Leipzig: Leopold Voss, 1896. Hermann von Helmholtz. Handbuch der physiologischen Optik. 3rd. ed., based on the text of the first, with supplementary material. A. Gullstrand, J. von Kries, and W. Nagel, eds. 3 vols. Hamburg and Leipzig: Leopold Voss, 1909- 1 1. Historical Studies in the P/iysical and Biological Sciences

xx

Abbreviations

JfruaM JHBS JHMAS Kirsten

Koenigsberger

MA

NTM PM SBB SBW SHPS VR3

WA WZHUB

Journal fur reine und angewandte Mathematik Journal of the History of the Behavioral Sciences Journal of the History ofMedicine and Allied Sciences Dokumente einer Freundschaft. Briefwechsel zwischen Hermann von Helmholtz und Emil du BoisReymond 1846-1894. Eds. Christa Kirsten, et al. Berlin: Akademie-Verlag, 1986. Leo Koenigsberger. Hermann von Helmholtz. 3 vols. Braunschweig: Friedrich Vieweg und Sohn, 1902-3. Muller's Archiv fur Anatomie, Physiologie, und wissenschaftliche Medizin Monatsberichte der Koniglich Preussischen Akademie der Wissenschajlen zu Berlin. NTM-Zeitschrift fur Geschichte der Naturwissenschaft, Technik und Medizin. Philosophical Magazine. Sitzungsberichte der Koniglich Preussischen Akademie der Wissenschaften zu Berlin. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. [Wien]. Mathematisch-Naturwissenschaft liche Classe. Studies in History and Philosophy of Science Hermann von Helmholtz. Vortrage und Reden. 3rd ed. 2 vols. Braunschweig: Friedrich Vieweg und Sohn, 1884. Hermann von Helmholtz. Vortrage und Reden. 4th ed. 2 vols. Braunschweig: Friedrich Vieweg und Sohn, 1896. Hermann von Helmholtz. Vortrage und Reden. 5th ed. 2 vols. Braunschweig: Friedrich Vieweg und Sohn, 1903. Wissenschaftliche Abhandlungen von Hermann von Helmholtz. 3 vols. Leipzig: J.A. Barth, 1882-95. Issue devoted to "Hermann von Helmholtz' philosophische und naturwissenschaftliche Leistungen aus der Sicht des dialektischen Materialismus und der modernen Naturwissenschaften." Wissenschaftliche Zeitschrift der Humboldt-Universitat zu Berlin, Mathematisch-Naturwissenschaftliche Reihe Zeitschrzjl fur Physikalische Chemie.

Chronological Listing of the Principal Events and Publications of Helmholtz's Life and Career

Birth (3 1 August) of Hermann Ludwig Ferdinand Helmholtz in Potsdam Enters Potsdam Gymnasium (Eastertime) Graduates Potsdam Gymnasium (September) Enters the Konigliches medicinisch-chirurgisches FriedrichWilhelms-Institut, Berlin, to study medicine and become a Prussian military medical doctor Defends dissertation-"De fabrica systematis nervosi evertebratorum"-and graduates medical school (October-November) Begins year-long internship at the Charit6 hospital, Berlin Begins service as army staff surgeon with the Konigliches Garde-Husaren-Regiment, Potsdam (October) "Ueber das Wesen der Faulniss und Gahrung," MA On leave in Berlin from army unit to prepare for state medical examinations (October - February); simultaneously conducts research in Gustav Magnus's private laboratory "Ueber den Stoffverbrauch bei der Muskelaction," MA Passes final state medical examination in February; returns to Potsdam to resume army duty "Warme, physiologisch," Encyclopadisckes Handworterbuch der medicinischen Wissenschaften Transfers to Konigliches Regiment der Gardes du Corps, Potsdam (June)

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Chronological Listing

"Bericht uber 'die Theorie der physiologischen Warmeerscheinungen' betreffende Arbeit aus dem Jahre 1845," Fortschritte der Physik Ueber die Erhaltung der Kraft. Eine physikalische Abhandlung 1848 Leaves military service (September) to teach anatomy at the Kunstakademie and serve as assistant to Johannes Miiller at the Anatomisches Museum, Berlin "Ueber die Warmeentwickelung bei der Muskelaction," M A "Bericht uber 'die Theorie der physiologischen Warmeerscheinungen' betreffende Arbeiten aus dem Jahre 1846," Fortschritte der Physik 1849 Appointed extraordinary professor of physiology at the University of Konigsberg Marries Olga von Velten (1826-59) 1850 "Ueber die Fortpflanzungsgeschwindigkeit der Nervenreizung," M B Birth of first child, Katharina ("Kathe") Caroline Julie Betty (1 850-77) "Messungen uber den zeitlichen Verlauf der Zuckung animalischer Muskeln und die Fortpflanzungsgeschwindigkeit der Reizung in den Nerven," MA Invents ophthalmoscope (October - December) "Bericht uber 'die Theorie der physiologischen Warmeerscheinungen' betreffende Arbeiten aus dem Jahre 1847," Fortschritte der Physik 1851 Appointed ordinary professor of physiology at the University of Konigsberg "Ueber die Methoden, kleinste Zeittheile zu messen, und ihre Anwendung fur physiologische Zwecke," Konigsberger naturwissenschaftliche Unterhaltungen Beschreibung eines Augenspiegels zur Untersuchung der Netzhaut in lebenden Auge "Ueber die Dauer und den Verlauf der durch Stromesschwankungen inducirten elektrischen Strome," AP 1852 Birth of second child, Richard Wilhelm Ferdinand (1852-1934) "Messungen iiber Fortpflanzungsgeschwindigkeit der Reizung in den Newen. Zweite Reihe," MA "Ueber eine neue einfachste Form des Augenspiegels," Vierordt 's Archiv fur Physiologische Heilkunde "Ueber die Theorie der zusammengesetzten Farben," AP Delivers habilitation lecture at Konigsberg University: "Ueber die Natur der menschlichen Sinnesempfindungen," Konigsberger naturwissenschajilicher Unterhaltungen

Chronological Listing

xxiii

"Ueber Herrn D. Brewster's neue Analyse des Sonnenlichts," AP

"Ein Theorem uber die Vertheilung elektrischer Strome in korperlichen Leitern," MB 1853 Attends meeting of the British Association for the Advancement of Science; first trip abroad "Ueber einige Gesetze der Vertheilung elektrischer Strome in korperlichen Leitern mit Anwendung auf die thierisch-elektrischen Versuche," AP Delivers first lecture on Goethe, before the Deutsche Gesellschaft, Konigsberg: "Ueber Goethe's naturwissenschaftliche Arbeiten," VR5:l "Ueber eine bisher unbekannte Veranderung am menschlichen Auge bei veranderter Accomodation," MB 1854 Death of mother, Caroline (1797-1 854) "Erwiderung auf die Bemerkungen von Herrn Clausius," AP Delivers lecture in Konigsberg: "Ueber die Wechselwirkung der Naturkrafte und die darauf bezuglichen neuesten Ermittelungen der Physik," VR5:l "Ueber die Geschwindigkeit einiger Vorgange in Muskeln und Nerven," MB 1855 Delivers Kant-Denkmal lecture in Konigsberg: "Ueber das Sehen des Menschen," VR5:l Appointed professor of anatomy and physiology at the University of Bonn "Ueber die Zusammensetzung von Spectralfarben," AP "Ueber die Empfindlichkeit der menschlichen Netzhaut fur die brechbarsten Strahlen des Sonnenlichts," AP "Ueber die Accomodation des Auges," A 0 1856 "Ueber Combinationstone," AP Handbuch der physiologischen Optik (Part 1) 1857 Appointed Corresponding Member of the Berlin Akademie der Wissenschaften "Das Telestereoskop," AP Delivers lecture in Bonn: "Ueber die physiologischen Ursachen der musikalischen Harmonie," VR5:l 1858 Appointed professor of physiology at the University of Heidelberg "Ueber Integrale der hydrodynamischen Gleichungen, welche den Wirbelbewegungen entsprechen," JfruaM "Ueber die subjectiven Nachbilder im Auge," Sitzungsberichte des naturhistorischen Vereins der preussischen Rheinlande und Westphalens

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Chronological Listing

"Ueber Nachbilder," Amtlicher Berichr uber die Versamrnlung deutscher Natutforscher und Aerzte Death of father, August Julius Ferdinand (1 792- 1859) Death of wife, Olga "Ueber die Klangfarbe der Vocale," AP "Ueber Luftschwingungen in Rohren mit offenen Enden," JfruaM "Theorie der Luftschwingung in Rohren mit offen Enden," JfruaM "Ueber Reibung tropfbarer Fliissigkeiten," SBW (with G. v. Piotrowski) Handbuch der physiologischen Optik (Part 2) Mames Anna von Mohl (1 834-99) Birth of third child, Robert Julius (1 862-89) Appointed prorector of the University of Heidelberg for 186263; delivers prorectoral address before the University: "Ueber das Verhaltniss der Naturwissenschaften zur Gesammtheit der Wissenschaften," VR5:l Delivers lecture series in Karlsruhe (1 862-63): "Ueber die Erhaltung der Kraft," VR5:1 "Ueber die Form des Horopters, mathematisch bestimmt," Verhandlungen des naturhistorisch-rnedicinischen Vereins zu Heidelberg Die Lehre von den Tonempfindungen als physiologische Grundluge fur die Theorie der Musik "Ueber die normalen Bewegungen des menschlichen Auges," A0 Birth of fourth child, Ellen Ida Elisabeth (1 864-1 94 1) Delivers lectures on the conservation of energy at The Royal Institution, London "Ueber den Horopter," A 0 "Ueber stereoskopisches Sehen," Verhandlungen des naturhistorisch-rnedicinischen Vereins zu Heidelberg Delivers lectures in Heidelberg and Frankfurt am Main: "Eis und Gletscher," VRi:l Populare wissenschaftliche Vortrage (Heft 1) Die Lehre von den Tonernpfindungen (2nd ed.) " ~ b e die r tatsachlichen Grundlagen der Geometrie," Verhandlungen des naturhistorisch-rnedicinischen Vereins zu Heidelberg Handbuch der physiologischen Optik (Part 3) Birth of fifth child, Friedrich ("Fritz") Julius (1868-1901) Delivers lectures in Frankfurt am Main and Heidelberg: "Die

Chronological Listing

1869 1870

1871

xxv

neueren Fortschritte in der Theorie des Sehens," VR5:I "Ueber die Thatsachen, die der Geometrie zu Grunde liegen," Nachrichten der koniglichen Gesellschaji der Wissenschaften zu Gottingen Delivers lecture in Innsbruck: "Ueber das Ziel und die Fortschritte der Naturwissenschaften," VR5:l Named Foreign Member, Berlin Akademie der Wissenschaften Delivers lecture in Heidelberg: "Ueber den Ursprung und die Bedeutung der geometrischen Axiome," VR5:2 "Ueber die Gesetze der inconstanten elektrischen Strome in korperlich ausgedehnten Leitern," Verhandlungen des naturhistorisch-medicinischen Vereins zu Heidelberg "Ueber die Theorie der Elektrodynamik. Erste Abhandlung. Ueber die Bewegungsgleichungen der Elektricitat fur ruhende leitende Korper," JfruaM "Ueber die Bewegungsgleichungen der Elektricitat fur ruhende leitende Korper," JfruaM Die Lehre von den Tonempjindungen (3rd ed.) Populare wissenschajiliche Vortrage (Heft 2) Appointed professor of physics at the University of Berlin and named Ordinary Member of the Berlin Akademie der Wissenschaften "Ueber die Fortpflanzungsgeschwindigkeit der elektrodynamischen Wirkungen," MB "Ueber die Zeit, welche notig ist, damit ein Gesichtseindruck zum Bewusstsein kommt, Resultate einer von Herrn N. Baxt in Heidelberger Laboratorium ausgefuhrten Untersuchung," MB

1872 1873

Delivers lecture in Berlin: "Zum GedachtniB an Gustav Magnus," VR-5:2 Delivers lectures in Heidelberg and Cologne: "Ueber die Entstehung des Planetensystems," VR5:2 Delivers lectures in Berlin, Dusseldorf, and Cologne: "Optisches iiber Malerei," VR5:2 "Ueber die Theorie der Elektrodynamik," MB Receives Orden pour le mkrite fur Kunst und Wissenschaft "Ueber die Theorie der Elektrodynamik. Zweite Abtheilung: Kritisches," JfvuaM "Vergleich des Ampkre'schen und Neumann'schen Gesetzes fur die elektrodynamischen Krafte," MB "Ueber galvanische Polarisation in gasfreien Flussigkeiten," AP "Ueber die Grenzen der Leistungsfahigkeit der Mikroskope," MB

xxvi

Chronological Listing

Receives Copley Medal from the Royal Society of London; and the Becquerel Medal, France "Ueber die Theorie der Elektrodynamik. Dritte Abhandlung: Die elektrodynamischen Krafte in bewegten Leitern," JfruaM "Die theoretische Grenze fur die Leistungsfahigkeit der Mikroskope," AP "Zur Theorie der anomalen Disperion," AP "Kritisches zur Elektrodynamik," AP "Ueber das Streben nach Popularisirung der Wissenschaft. Vorrede zur Uebersetzung von Tyndall's Fragments o f Science," VR5:2 "Induction und Deduction. Vorrede zum zweiten Theile des ersten Bandes der Uebersetzung von William Thomson's und Tait's Treatise on Natural Philosophy, VR5:2 1875 Delivers lecture in Hamburg: "Wirbelsturme und Gewitter," VR5:2 "Versuche uber die im ungeschlossenen Kreise durch Bewegung inducirten elektromotorischen Krafte," AP Populare wissenschaftliche Vortrage (Hefte 1 and 2, 2nd ed.; Heft 3) 1876 "Bericht betreffend Versuche iiber die elektromagnetische Wirkung elektrischer Convection, ausgefuhrt von Hrn. Henry A. Rowland," AP 1877 Appointed advisory editor on mathematical and theoretical physics papers for the A P Death of first daughter, Kathe Appointed professor of physics at his alma mater; delivers lecture before same: "Das Denken in der Medicin," VR5:2 Elected rector of the University of Berlin for the academic year 1877-78; delivers rectorai address before the University: "Ueber die akademische Freiheit der deutschen Universitaten," VR5:2 "Ueber galvanische Strome, verursacht durch Concentrationsunterschiede; Folgerungen aus der mechanischen Warmetheorie," A P Die Lehre von den Tonempfindungen (4th ed.) 1878 "Ueber die Bedeutung der Convergenzstellung der Augen fiir die Beurtheilung des Abstandes binocular gesehener Objekte," AP "Telephon und Klangfarbe," AP Delivers lecture to mark the Stiftungsfeier of the University of Berlin: "Die Thatsachen in der Wahrnehmung," VR5:2

1874

Chronological Listing

xxvii

"Ueber elektrische Grenzschichten," MB "Studien uber elektrischen Grenzschichten," AP 1880 "Ueber die Bewegungsstrome am polarisirten Platina," AP 1881 Receives honorary Doctor-of-Law degree, Cambridge University Delivers lecture (in English) before the Chemical Society, London: "Die neuere Entwickelung von Faraday's Ideen uber Elektricitat," VR5:2 Attends International Electrical Congress, Paris Delivers lecture before the Elektrotechnischer Verein, Berlin: "Ueber die Berathungen des Pariser Congresses, betreffend die elektrischen Maasseinheiten," Elektrotechnische Zeitschrift "Ueber die auf das Innere magnetische oder dielektrisch polarisirter Korper wirkenden Krafte," AP "Ueber galvanische Polarisation des Quecksilbers und darauf beziigliche neue Versuche des Herrn Arthur Konig," MB 1882 "Die Thermodynamik chemischer Vorgange," SBB "Zur Thermodynamik chemischer Vorgange," SBB Delivers lecture before the Physikalische Gesellschaft, Berlin: "Bericht iiber die Thatigkeit der internationalen elektrischen Commission," Verhandlungen der phvsikalischen Gesellschaft zu Berlin "Ueber absolute Maasssysteme fur elektrische und magnetische Grossen," AP Wissenschaftliche Abhandlungen (Volume 1) 1883 Ennobled by William I Appointed Honorary Member, National Academy of Sciences, Washington Participates in conference of the International Electrical Congress, Paris Participates in conference of the International Geodetic Congress, Rome Wissenschajiliche Abhandlungen (Volume 2 ) "Zur Thermodynamik chemischer Vorgange. Folgerungen, die galvanische Polarisation betreffend," SBB "Bestimmung magnetischer Momente durch die Waage," SBB 1884 Represents the Berlin Akademie der Wissenschaften at the 300th anniversary of the founding of the University of Edinburgh "Studien zur Statik monocyclischer Systeme," SBB "Prinzipien der Statik monocyklischer Systeme," JfruaM Vortrage und Reden (3rd ed., originally entitled Populare wissenschaftliche Vortrage) 1879

xxviii

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1885

Handbuch der physiologischen Optik (2nd ed., appears in parts between 1885 and 1895) Appointed Vice-Chancellor of the Friedensclasse of the Orden pour le mkrite fiir Kunst und Wissenschaft "Ueber die physikalische Bedeutung des Princips der kleinsten Wirkung," JfruaM Receives the first Graefe Medal, Ophthalmologische Gesellschaft, and delivers lecture in Heidelberg: "Antwortrede gehalten beim Empfang der Graefe-Medallie zu Heidelberg," VR5:2 "Zur Geschichte des Princips der kleinsten Action," SBB Delivers lecture in Berlin: "Josef Fraunhofer. Ansprache gehalten bei der Gedenkfeier zur hundertjahrigen Wiederkehr seines Geburtstages," VR5:2 "Weiter Untersuchungen, die Elektrolyse des Wassers betreffend," AP "Zahlen und Messen, erkenntnisstheoretisch betrachtet," Philosophische Aufsatze, Eduard Zeller zu seinern funfzigjahrigen Doctorjubilaurn gewidmet (Leipzig) Appointed first President of the Physikalisch-Technische Reichsanstalt; relinquishes full-time university teaching duties Appointed Honorary Member of the Imperial Russian Academy of Medicine "Ueber atmospharische Bewegungen," SBB Death of Robert von Helmholtz "Ueber atmospharische Bewegungen. Zweite Mitteilungen," SBB Represents the University of Berlin at the 600th anniversary of the founding of the University of Montpellier "Die Storung der Wahrnehmung kleinster Helligkeitsunterschiede durch das Eigenlicht der Netzhaut," Zeitschrift fur Psychologie und Physiologie der Sinnesorgane "Die Energie der Wogen und des Windes," AP Named "Wirklicher Geheimer Rat" with the predicate "Excellenz" by William I1 Public celebration of Helmholtz's 70th birthday; numerous honors received Serves as member on Prussian Commission on Issues of Higher Education "Erinnerungen. Tischrede gehalten bei der Feier des 70. Geburtstages," VR5:l "Versuch einer erweiterten Anwendung des Fechnerschen Ge-

1886

1887

1888

1889 1890

1891

Chronological Listing

1892

1893

1894

1895 1897

xxix

setzes im Farbensystem," Zeitschrift fur Psvchologie und Phvsiologie der Sinnesorgane "Versuch, das psychophysische Gesebz auf die Farbenunterschiede trichromatischer Augen anzuwenden," Zeitschrift .fur Psychologie und Physiologie der Sinnesorgane Celebrates fiftieth anniversary of receiving his medical degree Delivers second lecture on Goethe, before the Goethe Gesellschaft, Weimar: "Goethe's Vorahnungen kommender naturwissenschaftlicher Ideen," VR5:2 "Das Princip der kleinsten Wirkung in der Elektrodynamik," AP "Elektromagnetische Theorie der Farbenzerstreuung," AP Travels to America to serve as Germany's official representative at the International Electrical Congress in Chicago and tours America (August - October); sustains serious head injury on board ship while returning to Germany "Zusatze und Berichtigungen zu dem Aufsatze: Elektromagnetische Theorie der Farbenzerstreuung," AP "Folgerungen aus Maxwell's Theorie iiber die Bewegungen des reinen Aethers," A P Death (8 September); public memorial service held (12 December) in the Singakademie, Berlin "Uber den Ursprung der richtigen Deutung unserer Sinneseindriicke," Zeitschrzfi fur Psychologie und Phy.siologie der Sinnesorgane "Heinrich Hertz. Vorwort zu dessen Prinzipien der Mechanik," V R ~ : ~ Wissenschaftliche Abhandlungen (Volume 3) Vorlesungen uber Theoretische Physik, eds. Arthur Konig, et al. 6 vols. (Leipzig: J.A. Barth, 1897-1907).

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Introduction: Helmholtz at the Borders of Science David Cahan

Historians of modern science, philosophy, and cultural history have long recognized that Hermann von Helmholtz played a leading role in European cultural life during the second half of the nineteenth century. Helmholtz's genius profoundly altered his principal scientific disciplines of physiology and physics, and influenced the related disciplines of medicine, mathematics, physical chemistry, psychology, and meteorology. Philosophy and the fine arts of painting and music were also affected by his work. His views on science and society were listened to and solicited by ministers of state, and late in his career he participated in the interactions of science and industry. Perhaps the most striking feature of Helmholtz's thinking was the ability to link findings within a given cognitive domain or between two or more domains. Although he helped shape several disciplines, his abiding intellectual interests were transdisciplinary in nature: what most engaged him were general problems of energy transformation, human perception, understanding nature as a mechanical system, and the foundations and limits of science itself. Moreover, his scientific work occasioned and, to some extent was also contoured by, his articulation of epistemological views and a philosophy of science and mathematics; even the nature of aesthetic experience and the place and role of science in society came within his cognitive purview. In May 1871, shortly after assuming his new position as professor of Acknowledgments: I thank Jed Buchwald, Richard L. Kremer. R. Steven Turner, and (especially) Jean Axelrad Cahan for their comments on an earlier version of this Introduction.

2

Introduction

experimental physics at the University of Berlin, he wrote to the philosopher Benno Erdmann: I a m very glad that a better relationship between philosophers and natural scientists is again gradually developing, and hope that both [groups] will again become as close to one another as was once the case. I have always felt the need for such an alliance, since I have worked around the borders of science, in part on the most general geometrical a n d mechanical axioms on account of the conservation of force, in part o n the theory of perceptions.'

Helmholtz consistently pursued scientific problems that stood at the common boundary of two or more sciences, using the methods or techniques of one science to work on problems in another, and sought to integrate the sciences and philosophy by articulating the nature and consequences of science for philosophy. Although Helmholtz's work, like Darwin's and Einstein's, was characterized by the creation of overarching principles aimed at unifying large parts of the sciences, it differed from theirs in that it ranged across both the biological and the physical sciences. As a young man, Helmholtz (1821-94) had wanted to become a physicist. However, as he later reported his family's limited financial circumstances meant that preparing for a career in medicine was the closest that he could come to a life in ~ c i e n c eNevertheless, .~ his predilection for physics and his training in medicine, combined with a voracious intellect and ambition, and the propitious historical moment of post-1840 German science, ultimately allowed a scientific self-expression far broader than either Darwin or Einstein ever contemplated. Perhaps this was part of the meaning of Einstein's statement, quoted as the frontispiece to this collection of essays on Helmholtz, to Mileva Marie in August 1899: "I admire ever more the original, free thinker Helm[holtz]."3 One consequence of the broad range of Helmholtz's scientific research was, as several of the essays in this volume indicate, that his leadership in a given discipline was often short-lived. During the first 1. Helmholtz to Erdmann. Berlin, 6 May 1871, Sondersammlungen, Martin-LutherUniversitat Halle-Wittenberg,Universitats- und Landesbibliothek Sachsen-Anhalt, Sign. Yi 4 I 147. Cf. Gary Hatfield's essay "Helmholtz and Classicism: The Science of Aesthetics and the Aesthetics of Science," in this volume on 541. 2. "Erinnerungen," VRS2: 1-2 1, on 7-9. 3. Albert Einstein to Mileva MariC, early August 1899, in The Collected Papers of Albert Einstein, eds., John Stachel, et al., 2 vols. to date (Princeton: Princeton University Press, 1987), vol. 1: The Earbl Years, 1879-1902:220-21, quote on 220.

Introduction

3

half of his professional career, from the early 1840s to the late 1860s, Helmholtz forged a reputation as one of Germany's leading physiologists, medical scientists, and physicists. His pathbreaking discovery of the velocity of the nerve impulse in the late 1840s; his invention of the ophthalmoscope in 1850-51; his fundamental work on color theory and space perception in the 1850s and 1860s; and the completion of his historic, three-volume Handbuch der physiologischen Optik (1856-67) and epochal Die Lehre von den Tonempjindungen als physiologische Grundlage fur die Theorie der Musik (1863) placed him among Europe's leaders in physiology and medicine. Yet after 1867 he largely abandoned work in physiology and medicine; it is particularly noteworthy that physiological optics and acoustics developed without his active participation. With his move to Berlin in 1871, where he assumed one of the most important scientific posts in the new Reich, he was finally in a position to devote his full attention to physics. He had, of course, made his principal contribution to physics in 1847, with his essay on the conservation of force (energy), and again later in 1858, with a study on hydrodynamics. Yet during the 1850s and 1860s, as the centrality of energy physics became increasingly recognized, Helmholtz largely left development of that field to others. During the 1870s and 1880s he successively concentrated on studies in electrodynamics, chemical thermodynamics, the mechanical foundation of thermodynamics, and mechanics, making creative, critical contributions to each of these fields. But again his interest in each field waned relatively soon; specialists abandoned or transcended his ideas, and his leadership was assumed by others. Despite the critical nature of his contributions to electrodynamic theory, Helmholtz's electrodynamic ideas and viewpoint never spread very widely, and became pass6 after the late 1880s. Similarly, while his analysis of chemical thermodynamics helped paved the way for the new physical chemistry of the 1880s, and that on monocyclic systems helped clarify Ludwig Boltzmann's ideas on such systems, Helmholtz forsook further studies in these fields, both of which moved ahead without him. Much the same can be said for his more limited work in mathematics, psychology, and meteorology. Circa 1871, Helmholtz's reputation among his fellow scientists probably stood at its height; few if any could deny his scientific status and authority within and beyond the Reich. Yet though he did much important and creative scientific work during the second half of his career, the effects of his restless scientific self began to take their toll. Although his reputation continued to rise among the educated public after 1871, and although he became the very embodiment of German Wissenschaft, this reputation was increasingly dependent on his pre- 1871 work

4

Introduction

and on his institutional, political, and cultural standing in German science. Einstein's statement of 1899 notwithstanding, by the end of the century Helmholtz's stature was diminishing. The broad range of Helmholtz's scientific work has also had the somewhat unusual consequence that few if any scholars to date have been able or willing to analyze the entire range of Helmholtz's scientific work and to place it within its appropriate scientific and philosophical contexts. Helmholtz's principal biographer, Leo Koenigsberger, who was a good friend of the Helmholtz family and gained privileged access to private correspondence, attempted in his three-volume biography Hermann von Helmholtz (1902-3) to portray all of Helmholtz's scientific accomplishments and to narrate his life. But the work remains largely an uncritical assemblage of extracts from Helmholtz's published writings and unpublished 1ette1-s.~Of course there have been, as the Bibliography to the present volume attests, many valuable individual studies of selected aspects of Helmholtz's oeuvre. Yet there still does not exist a modern, critical treatment of the entire body of Helmholtz's work. The present volume of fifteen essays on Helmholtz seeks to meet precisely this historiographic goal. The essays describe, analyze, and interpret virtually all areas of his work: in medicine, heat and nerve physiology, color and vision theory, physiological optics and acoustics, energy conservation, electrodynamics, chemical thermodynamics, the mechanical foundation of thermodynamics, epistemology, philosophy of science and mathematics, and the relations of science and art and of science and society. Only studies of his relatively minor work in hydrodynamics and meteorology have been ~ r n i t t e d . ~

4. In addition to Koenigsberger, the other book-length biographies of Helmholtz are: John Gray McKendrick, Hermann Ludwig Ferdinand von Helmholtz (New York: Longmans, Green & Co., 1899); Julius Reiner, Hermann von Helmholtz (Leipzig: Theod. Thomas, 1905); Hermann Ebert, Hermann von Helmholtz (Stuttgart: Wissenschaftliche Verlagsgesellschaft, 1949); Petr Petrovich Lazarev, Helmholtz (in Russian) (Moscow: Akademia Nauk USSR, 1959); and A.V. Lebedinskii, U.I. Frankfurt, and A.M. Frank, Helrnhollz (1821-1894) (in Russian) (Moscow: Akademia Nauk USSR, 1966). A special issue of Die Naturwissenschaften, "Dem Andenken an Helmholtz. Zur Jahrhundertfeier seines Geburtstages," Die Naturwissenschaften 9:35 (192 1):673-711; and a volume edited by Heinrich Scheel, Gedanken von Helmholtz iiber schopferische Impulse und iiber das Zusammenwlrken verschiedener W~ssenschaftszweige( = Sitzungsberichte des Plenums und der Klassen der Akademie der Wissenschaften der DDR Nr. 1, 1972) (Berlin: Akademie-Verlag, 1972), contain collections of articles about various aspects of Helmholtz's work. 5. See, however, W.M. Hicks. "Report on Recent Progress in Hydrodynamics. Part I. General Theory," Report of the Fift-v-First Meeting of the British Association for the Adt5ancement of Science: Held at York in August and September 1881 (London: John Murray, 1882), 57-88; Karl-Heinz Bernhardt, "Der Beitrag Hermann von Helmholtz'

Introduction

5

This Introduction makes no pretense at either enumerating Helmholtz's many empirical scientific results and theoretical positions or at fully describing the interpretations of them by the contributors to this volume. It seeks instead to highlight two highly complex and, at points, interrelated themes that, as the volume's essays indicate, dominated various parts of Helmholtz's scientific work at various stages of his career: first, the combined use of instrumentation, measurement, and mathematical analysis to establish theoretical understanding; and second, a quest for intellectual synthesis. Particularly during the first half of his career, Helmholtz creatively and interactively used scientific instrumentation, measurement, and mathematics to advance understanding of physiological phenomena; he brought an unprecedented degree of analytical rigor to his subject. As Kathryn M. Olesko and Frederic L. Holmes demonstrate in their essay on Helmholtz's early physiological research, Helmholtz employed a variety of sophisticated instruments and apparatus-multiplicators, muscle-contraction apparatus and measuring devices, apparatus for measuring the propagation velocity of nerve impulses and a myograph-to conduct that research. Central to his construction of an empiricist theory of vision, as Timothy Lenoir argues, was his use of an ophthalmotrope for studying eye movement and an ophthalmometer for measuring the curvature of parts of the eye. His views on spatial perception, in particular on understanding the horopter problem and eye movements were, as R. Steven Turner shows, buttressed by his use of a series of simple instrumental demonstrations. And in his work in physiological acoustics, as Stephan Vogel shows, Helmholtz again employed a series of instruments-tuning-fork apparatus, spherical resonators, polyphonic sirens, and sound synthesizers and analyzers-that proved crucial for his study of the physiology of sound. Although Helmholtz made any number of improvements on or adaptations of these instruments, virtually all were invented by others. There was of course one important instrument which he invented himself and for which he first achieved renown, and with which his name has been associated ever since: the ophthalmoscope. In her essay on Helmholtz and the German medical community, Arleen

zur Physik der Atmosphare," WZFIUB 23t3 (1973):33 1-40; R. Wenger, "Helmholtz als Meteorologe," Die Na~urwissenschqfien 10 (1922):198-202; and Elizabeth Garber, "Thermodynamics and Meteorology ( 1850-1 900)," Annals of Science 33 (1976):s 1-65, esp. 60-3. See also Heinz Stiller, "Zur Bedeutung der Arbeiten von H. v. Helmholtz fur die geophysikalische Hydrodynarnik und fiir die Physik des Erdinnern," in Heinrich Scheel, ed., Gedanken von Hplmholtz. 45-8.

6

Introduction

Tuchman discusses the medical context in which Helmholtz worked and how the ophthalmoscope significantly changed medical diagnostics. She argues that Helmholtz used his invention of the ophthalmoscope (and, to a lesser extent, the ophthalmometer) to show how physicians and physiologists could help one another establish a scientific basis for medicine and physiology as an autonomous discipline. Although Helmholtz left the development of the ophthalmoscope to others, it continually redounded to his benefit, not least, as Lenoir shows, when practicing ophthalmologists subsequently used it to produce evidence in favor of his empiricist theory of vision. Helmholtz never lost sight of the larger purposes of scientific instruments: he built or had his instruments built in order to conduct measurements aimed ultimately at establishing laws and theories. At the same time, he consciously scrutinized the limitations of his instruments and measuring results, especially through mathematical data and error analysis. Olesko and Holmes show, for example, how Helmholtz used various quantitative techniques of precision as well as nonprecision measurement to determine the propagation velocity of the nerve impulse and to help convince his readers of his results. Through his rigorous, quantitative experiments on muscles; his precision measurements of heat formation in muscles; his precise, quantitative analysis of experimental error (especially the method of least squares); and his use of non-precision graphical analysis Helmholtz made a series of discoveries concerning muscular heat and nerve propagation velocity that simultaneously helped transform the very nature of experiment during the nineteenth century. Lenoir, again, shows that Helmholtz treated the eye itself as a measuring device which the brain uses to construct visual representations of the world with which it constantly interacts, and shows how Helmholtz used the principle of easiest orientation to analyze eye movement mathematically and to argue that the eye uses probability calculus for computing errors of eye motion. As the essays by Olesko and Holmes and by Lenoir show, Helmholtz brought the astronomer's and physicist's use of error analysis into physiology. Again, although markedly different from one another, Lenoir's and Turner's approaches to Helmholtz's deduction of Listings's and Donders's laws from the principle of easiest orientation respectively both call attention to Helmholtz's use of mathematics in physiology. Moreover, Vogel emphasizes Helmholtz's mathematical analysis of vowels, of the tone quality of musical instruments, and of sound perception. Finally, Robert DiSalle, in his essay on Helmholtz's empiricist philosophy of mathematics, analyzes the fundamental connection between Helmholtz's views on space perception and formal geometry, and how the latter developed out of the former: geometry,

Introduction

7

Helmholtz maintained, derived from physical measurement. It was no accident, as DiSalle points out, that Helmholtz began his work in geometry in 1866, just as he was bringing the final volume of the Handbuch to a close. Helmholtz's novel and exemplary employment of quantification and mathematical analysis in physiology was matched by its use in physics and chemistry, where it had a far more traditional and widespread use. In his analysis of the foundations of Helmholtz's electrodynamics, Jed Buchwald stresses the essential role of instruments and measurements for detecting the possible states of charged and currentcarrying objects along with their interaction or system energies. This search after new states and energies-what Buchwald calls "HelmholtzianismV-allowed Helmholtz and his students, above all Heinrich Hertz, to look for new effects or to study known effects in new ways. The Helmholtzian physical laboratory became, Buchwald argues, a site for using instruments to manipulate systems in order to see what new effects they might yield. Moreover, as both Helge Kragh's essay on Helmholtz's route to a theory of chemical thermodynamics and Giinter Bierhalter's on Helmholtz's mechanical foundation of thermodynamics indicate, during the 1880s Helmholtz brought an unprecedented degree of mathematical analysis to the study of chemical and thermodynamical phenomena. Indeed, as DiSalle argues, for Helmholtz there existed a deep connection between mathematics and the world of experience. Empiricism was an essential theoretical and philosophical viewpoint for Helmholtz. Turner argues that Helmholtz's conflict with Ewald Hering over the sources of human spatial perception essentially created the famous nativist-empiricist controversy. That conflict, and its contemporary scientific context, Turner maintains, did as much to shape Helmholtz's approach to spatial perception as did commitment to any empiricist philosophy. The third part of Helmholtz's Handbuch, Turner argues, is in no small measure an exercise in scientific rhetoric, aimed at once to defend empiricism, refute Hering, and draw new theoretical outlines for the field. In a similar vein, Vogel argues that Helmholtz's empiricist epistemology developed as an organizing principle for and during his research in physiological acoustics (as well as optics). The central feature of his empiricist epistemology, Vogel holds, was the division of the sensory process into three parts: the physical, the physiological, and the psychological. Both Turner and Vogel regard Helmholtz's empiricist epistemology as much more a product of his daily scientific research than of specific philosophical precommitments on his part. Helmholtz's empiricist philosophy of mathematics, DiSalle finds, shows a strong interaction between mathematical and empirical

8

Introduction

truths yet did not simply reduce mathematical truths to empirical ones. Instead, DiSalle argues that Helmholtz's empiricist philosophy of mathematics was based on a strong interaction between the psychological processes underlying mathematics and the laws governing the objective natural world. Finally, Michael Heidelberger argues that empiricism-more precisely, experimental interactionism-was one of the two central features of Helmholtz's philosophy of science (the other being metaphysical realism). As an experimental interactionist, Helmholtz believed that knowledge could only be gained by intervening in nature: scientists and others must manipulate parts of the world to gain knowledge about it. The essays by Lenoir, Buchwald, and DiSalle well illustrate how this "experimental interactionism" worked in practice. Helmholtz's quest for intellectual synthesis is the second overarching theme of the essays in this volume. His work attempted syntheses both within given disciplines and between parts of different disciplines with one another. In Fabio Bevilacqua's essay we see that Helmholtz's epochal study Ueber die Erhaltung der Kraft ( 1 847) represents an initial intellectual synthesis. Helmholtz here first emerged as a theoretical physicist, Bevilacqua argues, by combining a series of mechanical concepts and principles that had developed since the seventeenth century so as to deduce from them a version of the principle of conservation of force (energy), and by displaying a sophisticated methodology that distinguished clearly between theoretical and experimental physics. Moreover, Bevilacqua demonstrates precisely how Helmholtz applied his principle to a series of otherwise disparate topics in mechanics, heat, electricity, and magnetism, thereby helping to unite problems dispersed throughout physics. The essay of 1847, Bevilacqua argues, presented neither experimental nor mathematical novelties; it was, instead, intended as a study in and about theoretical physics. Though the precise relationship between his concurrent, heavily experimental, work in sensory physiology and that on the conservation of force remains unclear, there can be little doubt, as Bevilacqua points out, that Helmholtz hoped to apply his principle of force conservation to organic as well as inorganic nature. Like Bevilacqua, Richard L. Kremer argues that the distinctive feature of Helmholtz's work in color research was his inclination and ability to theorize and synthesize. While acknowledging Helmholtz's skill as an observer and experimenter, Kremer shows that in his color research Helmholtz neither presented new fundamental observations nor employed new instruments. Rather, during the 1850s he exploited his deep understanding of physical optics to clarify old problems like

Introduction

9

absorption and color mixing while developing a theory of color vision that synthesized ideas first put forth by a series of nineteenth-century physicists and physiologists. In so doing, he again, as in his physical study of the conservation of force, united a set of disparate physiological phenomena. As a consequence, theories of color ultimately became theories of color vision. At the same time, Kremer shows that Helmholtz's theory of color was intellectually bifurcated: to explain simultaneous contrast, he ultimately resorted to psychological as well as physiological language. Kremer argues that while Helmholtz's synthesizing efforts indeed united a range of previously unrelated physical and physiological phenomena into a coherent whole, his combined use of psychological and physiological explanations also produced a measure of controversy and incoherence that haunted color theorists for the remainder of the century. Helmholtz's work in space perception and physiological acoustics during the 1850s and 1860s further demonstrate his synthesizing efforts. In their different ways, both Lenoir and Turner argue that Helmholtz brought theoretical order to the study of eye movement and to the visual perception of space. Helmholtz's principle of easiest orientation linked physiology, physics, and psychology. And Vogel stresses the synthetic nature of Helmholtz's work in physiological acoustics: he shows that Helmholtz consciously set out to reform the entire field, developing theories of combination tones, consonance and dissonance, tone quality, and hearing which together were meant to constitute part of a larger theory of perception. From the late 1860s onwards, when he essentially abandoned physiological research, Helmholtz devoted himself largely to theoretical work in physics, although he did still direct important experimental work in his laboratory. He had earlier shown himself to be a good experimental physiologist and placed considerable importance on the role of empirical work; that emphasis now faded. Indeed, even within physiology the Handbuch derphysiologischen Optik and Die Lehre von den Tonernpfindungen als physrolog~scheGrundlage fur die Theorie der Musik already marked his theoretical, synthesizing tendency; they are in effect theoretical treatises that brought order to their fields and helped establish future research problems for specialists. It is thus not altogether surprising to see that when Helmholtz turned to physics full time, he did so largely as a theorist. In electrodynamics, as in his earlier work on the consewation of force, he aimed above all to bring order to a confusing field and to do so through the prosecution of theory rather than experiment. In his essay, Walter Kaiser argues that Helmholtz's work was crucial to the formation of classical electrodynamics. Although Helmholtz failed to convince many others of

10

Introduction

the validity of his own electrodynamic theory, he nonetheless did much to shape the field during the 1870s by calling attention to the shortcomings of Wilhelm Weber's theory and to the strengths of James Clerk Maxwell's, by proffering his own electrodynamic theory, and by directing his star student Heinrich Hertz to the field. As Kaiser shows, Helmholtz helped clarify and unify classical electrodynamics. At the same time, Helmholtz sought to unite electrodynamics and energy conservation, and, late in his career, to use the principle of least action to derive Maxwell's equations, here again seeking to bring disparate fields together. Jed Z. Buchwald approaches Helmholtz's electrodynamics rather differently. He argues that Helmholtz's work in electrodynamics led him to reconceive the entire field of physics. Helmholtz came to view physics as the science of interacting objects whose physical states at any moment in time determine their energy systems. Helmholtzianism, according to Buchwald, was a way of doing physics, not a theory: it allowed physicists to operate on the micro-level without making any particular assumptions about the nature of micro-level objects; it eliminated both Weberian forces and Maxwellian fields and replaced them with energy systems; it stressed measurement (i.e., interaction energies) but deemphasized precision; and, because it required the perturbation of systems, it heightened experimentalists' awareness of potential new effects and encouraged their search after them. For Helmholtz, Buchwald argues, the aim of physics became the determination of object states and their interaction energies, or what Buchwald calls a taxonomy of interactions. Helmholtzianism stressed the relations between objects; found its intellectual source largely in British energy physics (especially that of William Thomson and Peter Guthrie Tait); and designated as its avowed enemy the romantic, anti-British approach to physics practiced by Weber's student, Friedrich Zollner. The increasingly abstract character of Helmholtz's work became evident through the 1880s. In the early 1880s, as Helge Kragh shows, Helmholtz pioneered a theory of chemical thermodynamics. Building on his much earlier work in physiological chemistry, energy conservation, electrochemistry, and electrolytic conduction, Helmholtz introduced the concept of "free energy" to develop a thermodynamic theory of chemical change. In chemistry, as in much of his physics, Helmholtz conducted little experimental work. Instead, he pursued theoretical lines of inquiry, helping to transform chemistry from a static into a dynamic science. In so doing, as Kragh further argues, Helmholtz helped legitimize theoretical chemistry as a subdiscipline and pave the way for the new physical chemistry, towards which ironically he came to show much skepticism.

Introduction

11

In 1884 Helmholtz turned to the foundation of thermodynamics itself. As Bierhalter shows, Helmholtz sought to give a mechanical interpretation to thermodynamics. Using the highly abstract concept of monocyclic systems, he investigated the properties of these systems and their relation to heat theory. If nothing else, his study of monocyclic systems stimulated similar work by Boltzmann, which led to a critique of Helmholtz's own analysis. Ultimately, Bierhalter argues, Helmholtz aimed to refound the mechanical view of nature, to provide a mechanical understanding of all natural processes. He spent much of the last decade of his life (vainly) trying to use the principle of least action as the means to provide a unified view of all nature's forces, a new mechanical world picture. The late 1860s marked a sea change in Helmholtz's philosophical thinking as well as in his areas of interest. The second half of his career found him almost exclusively theoretical in his scientific work but also more explicitly philosophical. In addition to his rethinking the goals of physics (Buchwald) and the nature of mathematics and its relation to the empirical world (DiSalle), Helmholtz now began to articulate his philosophy of science as well. Michael Heidelberger argues that, along with the well-known influence of Kantian epistemology on Helmholtz's philosophy of science, there were other discernible influences. While Kant's metaphysics of nature, with its abstract, a priori notions of force and matter as necessary general concepts of science, led the early Helmholtz to advocate metaphysical realism (i.e., that science deals with a reality hidden from human senses), in the late 1860s, mainly under the influence of Michael Faraday's empiricist views of force and matter, Helmholtz began to consider forces not as necessary abstractions hidden behind the appearances but rather as hypothetical lawful relations among the appearances. At the same time, Heidelberger further maintains, the influence of Johann Gottlieb Fichte's philosophy of action provided Helmholtz with a methodology that Heidelberger calls "experimental interactionism": our knowledge of the external world can only be gained through intervening in nature. Hence the central features of Helmholtz's mature philosophy of science became metaphysical realism and experimental interactionism; it was a philosophy of science, Heidelberger concludes, which had much to do with idealism and relatively little with materialism or positivism. Helmholtz also endeavored to relate science and art and to demonstrate the utility of science for modern society. His attempt to explore the common ground of science and art is, for example, evident in the title of his book Die Lehre von den Tonempfindungen als physiologische Grundlagefur die Theorie der Musik. Gary Hatfield's essay shows just how Helmholtz sought to apply sensory physiology and

12

Introduction

psychology to music and painting and how far Helmholtz thought science could go towards explaining aesthetic phenomena. Hatfield argues that Helmholtz's perception of the boundaries between science and art led him to a general distinction between the Naturwissenschaf ten and the Geisteswissenschaften and resulted in an (at best) prototheoretical aesthetics, one which placed severe limits on the explanatory powers of natural science for art but which stressed the importance of historical analysis for elucidating aesthetic principles. Hatfield further explores Helmholtz's comparison of the artist's and the scientist's cognitive activity by analyzing Helmholtz's psychological theories of "unconscious inference" and "artistic intuition." He maintains that the former theory resulted in Helmholtz's "classicist" aesthetics of scientific explanation and the latter in a naturalistic solution to one of the nineteenth century's primary aesthetic problems, that of the relation between thought and feeling or understanding and imagination. Hatfield concludes that for the mature Helmholtz both science and art are united in their aim of finding universal truths (the lawful or the ideal) amongst changing phenomena and that both do so above all through their use of the imagination. Helmholtz's scientific work also provided the basis for his reflections on science and society. In this volume's final essay, the editor analyzes Helmholtz's numerous popular addresses on science and on science's relations with society. He argues that despite their diversity these addresses reveal an underlying, recurring theme of the civilizing power of science. More particularly, he argues that for Helmholtz a complex of four intimately related categories constitute the civilizing power of science: First, Helmholtz believed that science provides humankind with the capacity to understand the natural world and its place in it; second, that it enables humankind to control the world; third, that it forms the foundations for aesthetic life; and fourth, that it could help unite individuals socially and bind them to the larger polity of the nation-state. Though Helmholtz's views on science and society in good measure represented those of many nineteenth-century German liberals, he also spoke in part for the conservative German academic and cultural elite. The editor argues that Helmholtz sought to modernize the elite's understanding of the relations of scientific, socioeconomic, and political life by explaining to them the nature and institutional conditions for scientific advance; in turn, he hoped that they might understand his vision of the importance and centrality of natural science for building a modern industrial economy and for strengthening community bonds by stressing the importance of a rational (law-governed) world order and by forming an

Introduction

13

enlightened German citizenry. The complex theme of the civilizing power of science, then, was a grand, unifying vision of science and society, one fully worthy of the polymath who for over fifty years worked on the borders of science using instruments, measurement, and mathematics to establish new scientific theories, to synthesize the sciences, and to relate science and art.

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Part One Physiologist

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Helmholtz and the German Medical Community Arleen Tuchman

1. Introduction "Medicine," Helmholtz wrote in 1877, "was once my intellectual home, the one in which I grew up, and the wanderer best understands and is best understood in his native land."' Yet only rarely does one think of Hermann von Helmholtz in a medical context. The traditional image of Helmholtz is rather of a scientist whose broad-ranging intellectual interests brought him into contact with physicists, physiologists, mathematicians, philosophers, and other learned individuals. Yet, as the above quotation indicates, Helmholtz began his intellectual wanderings within the nineteenth-century German medical community; he even practiced hospital medicine for five years before receiving his first academic appointment at the Berlin Akademie der Kiinste in 1848. From that point on Helmholtz never again practiced medicine, yet, as this essay seeks to demonstrate, his ties to the German medical community remained strong for most of his career. Not only did several of his discoveries-foremost among them his invention of the ophthalmoscope in 1850-5 1-have a direct impact on medical practice; his methodological approach to the study of nature influenced the medical community as well. Medical reformers in particular praised

Acknowledgments: I would like to thank David Cahan for his advice and criticism. The research for this paper stemmed in part from two larger projects funded by the Fulbright Commission and the National Science Foundation. I . "Das Denken in der Medizin." in L'R' 2:165-93. on 170.

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Physiologist

the "new spirit of physiology," convinced that Helmholtz (and other experimental scientists) would help transform medicine into an exact science by teaching students new critical methods of analysis that would later be applicable to the study of disease. The German medical community clearly benefited from Helmholtz's contributions, but, as this essay also aims to show, Helmholtz profited as well. Section 2 focuses on his early years in Berlin and Potsdam (1838-48), demonstrating that through his studies at the Konigliches medizinisch-chirurgsche Friedrich-Wilhelms-Institut and at the University of Berlin, and through his tenure as a staff surgeon to the Royal Hussars in Potsdam, he received perhaps the best medical education and training then available in Germany. According to Helmholtz's own account, this medical training influenced his early work and career. Section 3 examines this claim, turning specifically to the events surrounding his invention of the ophthalmoscope and its reception by the medical community. The ophthalmoscope significantly altered medical diagnostics, having its greatest impact on a growing number of physicians with specialist interest in ophthalmology. Keenly aware of the ophthalmoscope's diagnostic importance, Helmholtz actively publicized his instrument. Indeed, he frequently announced to the medical community the potential practical applications of his scientific work. His reasons for doing so, as Section 3 further shows, derived from his appreciation of the ways in which physicians and physiologists could mutually benefit one another. New instruments and the experimental method would help establish medicine on a scientific basis, at the same time that physicians would help physiologists in their fight to establish an autonomous discipline of physiological science. Seeking institutional support in the university medical faculties, Helmholtz and other experimental physiologists realized that their success rested in part on their ability to convince university and state administrators that their work was of potential significance to the medical community. The importance of this strategy becomes evident in Section 4, which focuses on the events surrounding the institutionalization of experimental physiology at the University of Heidelberg and Helmholtz's appointment to a newly created chair for this subject in 1858. This appointment, it is argued, occurred squarely within a medical context, with Helmholtz remaining the favored candidate during a protracted period of negotiation largely because of his perceived link to the medical community, a perception that Helmholtz desewed-and cultivated. This essay argues neither that Helmholtz is best understood within the nineteenth-century German medical community nor that his primary motivation in his early career was to improve medical practice.

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19

Both claims are false. Throughout his years at Konigsberg, Bonn, and Heidelberg, Helmholtz's intellectual interests centered on discovering the chemical and physical laws underlying physiological processes, and on determining the physical and philosophical foundations of sensory perception. Nonetheless, Helmholtz seldom lost sight of the potential practical applications of the knowledge he produced. He may only occasionally have pursued such practical applications himself, yet he appreciated and publicized them when they occurred, both recognizing the support he could win from the medical community and appreciating, like most individuals involved in "pure" research, that nothing better demonstrated the legitimacy of a scientific theory than the ability to derive practical consequences from it. Thus Helmholtz's motives for maintaining strong ties to the German medical community were both professional and intellectual, and they were ties he actively encouraged during the twenty-two years he spent as a member of German university medical faculties.

2. Helmholtz's Medical Education in Berlin and Practice in Potsdam, 1838-48 During his early teenage years. Helmholtz developed an interest in the natural sciences, particularly in physics. In the 1830s, however, pursuit of a career in science was difficult. Although some hoped to forge a link between scientific research and industrial advance, the German economy gave but scant support to scientific careers, and only a few individuals received academic appointments in the natural sciences. Consequently, more than a few who wanted to study the natural sciences chose instead to pursue medicine. This, at least, was the path Helmholtz selected, and in 1838, at the age of seventeen, he moved from Potsdam to Berlin to begin his medical studies at the Konigliches medizinisch-chirurgische Friedrich-Wilhelms-Institut (formerly called the Pepiniere), a medical school designed specifically for the training of military physicians.* The Institut gave promising young men of insufficient financial means the opportunity to pursue a medical career. This arrangement greatly benefited Helmholtz, whose father, a Prussian Gymnasium teacher, reportedly did not earn enough to finance a university education for his son. Taking advantage of family connections to Christian 2. Biographical information on Helmholtz is taken from Koenigsberger 1; and R. Steven Turner, "Hermann von Helmholtz," DSB 6:241-53. On the Institut, see Dr. Schickert, Die ~nilitararztlichenBildungsanstalten von ihrer Griindung his zur Gegenwart (Berlin: Ernst Siegfried Mittler und Sohn. 1895).

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Physiologist

Ludwig Mursinna, General Surgeon of the Prussian Army between 1789 and 1809 and professor of surgery at the CharitC (the Berlin city hospital) and the Pepini6re until 1820, in 1837 Helmholtz's father sought admission for his son to the Institut. Although Helmholtz's first love was physics, he was not, by his own admission, "at all opposed to the study of living nature."' There, as in the study of inorganic nature, he saw the possibility of pursuing the study of the causal relations among phenomena. In the fall of 1838, having received a stipend from the Institut, in exchange for which he promised to serve eight years in the Prussian military, Helmholtz left for Berlin, hoping that in the course of his medical education he might satisfy his scientific curiosity as well. His hopes were not unfounded. German medical education during the 1830s was very much in transition. Whereas professors had previously focused their lectures on the recitation of a text (often their own), several now began to embellish their lectures with demonstrations and experiments. Among the younger lecturers and professors it was also not uncommon to provide instruction in microscopical, chemical, and even diagnostic skills. In the early 1830s, for example, Johann Lukas Schonlein, one of Germany's most prominent clinicians, encouraged his young assistants to provide instruction in the use of the stethoscope to medical students at the University of Wiirzburg.4 (In 1840, Schonlein moved to the University of Berlin, where Helmholtz attended his classes.) Later in the decade, Jacob Henle, Privatdozent in general pathology and general anatomy at the University of Berlin, offered a class in microscopical techniques for which sixty students enrolled. Shortly thereafter, Privatdozenten at the universities of Bonn and Tiibingen offered courses "in the use of the microscope" as well. By the early 1840s universities throughout Germany provided basic instruction in the chemical and microscopical investigations of normal and pathological specimens as well as in the new techniques of auscultation and p e r c u ~ s i o n .Yet ~ despite these 3. "Erinnerungen," in VR5 1: 1-21, on 9. 4. On Schonlein, see Johanna Bleker, Die .hraturhistorrscheSchule 1825-1845. Ein Beitrag zur Geschichte der klinischen Medizin in Deutschland (Stuttgart: Gustav Fischer, 198 1). On Helmholtz on Schonlein, see his letters of 12 May 1840 and 16 January 1843 to his parents in David Cahan, ed. Letters ofHermann von Helmholtz to His Parents: The Medical Education of a German Scientist. 1837-1846 (Stuttgart: Franz Steiner Verlag, 1993), 76-7, 98-9, resp. 5. Josef Kerschensteiner, Das Leben und Wirken des Dr. Carl von Pfefer (Augsburg: Lampart & Co.. 1871), 9; Friedrich Merkel, Jacob Henle. Ein deutsches Gelehrtenleben (Braunschweig: Vieweg, 1891), 154-55, and W. Waldeyer. "J. Henle. Nachruf," Archiv f i i r mikroscoprscheiinatomie 26 (1 886):i-xxxii, esp. iii. The two Privatdozenten at Bonn and Tiibingen were August Meyer and Wilhelm Grube, respectively. (See Konrad KlaB,

Helmholtz and the German Medical Community

21

important first steps toward introducing "practically" oriented courses into the medical curriculum, most universities still lacked adequate facilities for students interested in going beyond basic instruction so as to perfect their skills or conduct their own research. Small laboratories, minimal equipment and instruments (Henle had only a few microscopes for instructing a class of sixty students), and small university clinics made it difficult for most students to work directly with patients. Consequently, many students intent on increasing their clinical experience spent some time abroad in one of the large clinics in Vienna or Paris. Still, in comparison to other German cities Berlin had much to offer. First, because it was a larger city it had more sick individuals to fill its clinical teaching wards. More to the point, it had, in addition to its university, several medical institutions and hospitals in its midst, including the Theatrum anatomicum (anatomical theater), the Collegium medico-chirurgicum, the Botanischer Garten, the Charit6 hosDesigned primarily for the pital, and the Friedrich-Wilhelms-In~titut.~ training of military physicians, all but the last of these institutions dated back to the reign of Frederick William I (17 13-40), the so-called Soldier-King. Concerned about the heavy medical losses suffered annually by his beloved army, Frederick William instituted several measures to improve the quality of medical care available to his soldiers. He converted his father's Orangerie into the Botanischer Garten; founded the Theatrum anatomicum for public dissections (1713) and the Collegium medico-chirurgicum for theoretical instruction (1 723); and established the Chant6 for clinical training (1 726). To some extent these institutions served civilian students of medicine and surgery, yet their primary purpose was to train an advanced corp of surgeons who could supervise medical affairs in each of the army's regiments. To this end, each year eight young men received three-year fellowships to study at the Collegium. This educational system remained largely unchanged until the end of the century when, with the increasing militarism of the Prussian state, the need for more trained army surgeons grew. To meet these needs Frederick William I1 founded another medical school in 1795, the Pepiniere, renamed the Konigliches medizinisch-chirurgische Friedrich-Wilhelms-Institut in 1818. This new state

Die Einfuhrung besonderer Kurse fur Mikroskopie und physikalische Diagnostik (Perkussion und Auskultation) in der rnedizinischen Unterricht an deutschen Universitaten im 19. Jahrhundert [Med.diss., Gottingen, 19711.) 6. For a discussion of these institutes see Paul Diepgen and Edith Heischkel, Die Medizin an der Berliner Charit4 his zur Grundung der Universitat (Berlin: J . Springer, 1935), and Schickert, Die militiirarztlichen Rildungsanstalten.

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Physiologist

medical institute accommodated and financed the education of between eighty and ninety pupils per year; in return, its graduates obligated themselves to serve as military surgeons in the Prussian army for eight years.' Although a student of the Institut, Helmholtz attended many classes at the University of Berlin. The two institutions had not always had close connections. In the years immediately following the founding of the university in 1810, the latter and the Institut had, due to their different goals, a tense relationship. The military medical institute had a practical goal-the training of medical surgeons for the Prussian army; by contrast, the university, founded on neo-humanist principles, sought to provide an environment that would awaken a spirit of inquiry in student^.^ Devotion to Wissenschaft, not to utilitarian or professional goals, defined the educational process. This process was dynamic, and had little to do with absorbing factual information. The teacher sought to arouse student curiosity while providing them with the proper critical tools for pursuing their new-found interests. The goal was to cultivate the individual's character; specific concrete achievements mattered little. Despite their different goals, efforts to keep the university and the Institut separate soon failed. A few years after the university opened its doors, several members of the medical faculty, including the professor of surgery, Carl Ferdinand von Graefe, and the professors of anatomy, Christoph Knape and Karl Asmund Rudolphi, accepted adjunct positions on the professorial staff of the Institut-for which they received handsome h ~ n o r a r i aThe . ~ gradual breakdown of the bamers dividing the two institutions occurred not least because the new university was not simply modelled after the neo-humanists' vision. Its absolute dependence upon the state, cemented by the financial bond, as well as the state's urgent need for well-educated civil servants, physicians, and teachers, guaranteed that utilitarian concerns were not totally absent from university education.I0 By 1825 students of the two 7. Schickert, Die militdrarztlichen Bildungsanstalten, 5, 49. 8. On neo-humanism see Helmut Schelsky, Einsamkeit und Freiheit. Idee und Gestalt der deutschen Universitat und ihrer Reformer, 2nd ed. (Diisseldorf Bertelsmann Universitatsverlag, 1971). On tensions between the university and the Institut see Arleen Tuchman, "Spannungen und Zusammenarbeit zwischen der Chant6 und der Berliner Universitat in der ersten Halfte des 19. Jahrhunderts," unpublished paper, read at the Deutsche Gesellschaft fur Geschichte der Medizin, Natunvissenschaft und Technik, Bayreuth, September 1987. 9. Memorandum from Johann Wilhelm Wiebel, Chef des Milit;imedicinalwesens, to Karl Freiherr Stein zum Altenstein, head of the Ministerium des Innern, 10 April 1827, in Geheimes Staatsarchiv PreuBischer Kulturbesitz, Merseburg, Ministerium des Innern, Rep. 76 VIIIB, Nr. 4419, B1.78. 10. The best treatment of the various interests surrounding the founding of the University of Berlin is Charles E. McClelland, State, Societv, and C1niversity in Germany.

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23

institutions shared many of the same medical and scientific institutes, and attended many classes together, listening to the same lectures from members of the university faculty. Not all differences between the two institutions had disappeared, however. Whereas Lernfreiheit and Lehrfreiheit characterized university education, the course of study at the Institut was highly regimented. During the first of four years of instruction, students attended lectures on osteology, splanchnology, physics, botany, chemistry, physiology, general anatomy, and natural history. In the second year they continued to study these subjects, to which were added pathology and pharmacy, along with courses in anatomical dissection aimed at complementing their theoretical lectures. In the third year they advanced to general and special therapeutics, semiotics, surgery, and obstetrics. And in their fourth and final year they attended the polyclinic and the surgical, medical, ophthalmological, and obstetrical clinics in the CharitC. Following this rigid four-year course of medical instruction, they spent a further year in the CharitC doing rotation in the various wards. Although prohibited from treating their own patients, their duties were extensive. Under the supervision of the graduates of the Institut, they prescribed and administered medicines according to their superiors' orders; wrote case histories; and supervised the nursing staff in all hygienic matters." Thus, at a time when university students had to go to Paris or Vienna to acquire extensive clinical experience, Institut students received extensive surgical and clinical training in the wards of a large city hospital. Helmholtz valued the extensive medical training he received-indeed, he later attributed part of his success in inventing the ophthalmoscope to this training-but his real interests remained in the natural sciences, particularly in scientific research, which he pursued whenever opportunity availed.I2 Especially important here was his contact with Eilhard Mitscherlich, professor of chemistry at the university, and, above all, with Johannes Miiller, professor of physiology. Berlin hired Miiller in 1833 to help reform its medical faculty and to lend more support to a new direction in scientific research, one

1700-1914 (Cambridge and New York: Cambridge University Press, 1980), chap. 4. I I. Schickert, Die militararztlichen Bildungsanstalten, 33-6, 48. See, also, Helmholtz's letter to his parents of 5 May 1839, in which he describes the forty-two hours of classes required of him during the second semester of his first year of study, in Cahan, ed., Letters, 56-60. 12. Helmholtz's appreciation of his medical education is evident in his letters of 7 and 16 October, 16 November, 8 and 19 December 1842, and 16 January 1843 to his parents, in Cahan, ed., Letters, 92-3, 93-4, 95, 95-6, 96-7, 98-9, resp.; and below, Section 3.

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Physiologist

that moved beyond simple observation to the "creation of new phenomena through experiment."13 This new direction appealed to Helmholtz, too; in 1841 he decided to write a dissertation under Muller's supervision. For this purpose he scraped together his savings and bought his first instrument-a microscope.14 Displaying no sign of his later aversion toward microscopical research, Helmholtz investigated the structure of the nervous system in invertebrates, discovering that the nerve fibers originate in the ganglionic cells.15These cells had first been discovered in 1833 by the German physiologist Christian G. von Ehrenberg, who managed only to speculate that they give rise to nerve fibers; Helmholtz demonstrated the connection and suggested thereby that ganglia are more important developmentally than nerve fibers. Helmholtz's first contribution to the scientific community was thus a significant one, and it was made in microscopic anatomy. Although this initial finding impressed Muller, he asked Helmholtz to investigate several more animals before submitting his dissertation so as to demonstrate his thesis conclusively. To this end, Miiller offered him access to workspace in his anatomical museum. Every year Muller made such offers to a few talented students whose independent research he wished to encourage. Yet he could not provide them with much assistance. Compared to the research laboratories built in Germany after mid-century, the museums and laboratories of the early nineteenth century were extremely modest, usually consisting of only a few small rooms equipped with the simplest of equipment and instruments. Miiller's museum, with its cramped quarters, few instruments (beyond microscopes), and small budget was typical.'Qtill, his museum provided a virtually unmatched intellectual atmosphere, allowing talented students to work and to discuss their ideas with one another. In the 1830s the list of medical students who frequented Muller's museum included Jacob Henle, Theodor Schwann, and Robert Remak, all important contributors to the cell theory; in the 1840s they were followed by Rudolph Virchow, Emil du Bois-Reymond, Ernst Briicke, and Hermann Helmholtz. Although all these individuals made outstanding contributions to physiological research, their emphases differed. Several, particularly 13. Manfred Stiirzbecher, "Zur Berufung Johannes Miillers an die Berliner Universitat," Jahrbuchfiir die Geschichte Mittel- und Ostdeutschlands 21 ( 1 972): 184-226, quote on 193. 14. Koenigsberger 1:52. 15. De Fabrica systematis Nervosi Evertebratorum (Med. Diss., Berlin, 1842), in WA 2663-79. 16. Axel Genz, Zur Emanzipation der naturwissenschaftlichen Physiologie in Berlin (Med. diss. Magdeburg, 1976).

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Henle and Virchow, became leaders of the medical reform movement that flourished in Germany in the 1840s." They sought to give medicine a scientific basis by demonstrating that disease was nothing more than a deviation from normal physiological processes brought about by abnormal conditions. Convinced that physiological processes followed deterministic laws of nature, they argued that scientific medicine should aim at ascertaining how bodies, subject to these laws, behave under altered (i.e., abnormal) conditions. In their vision of scientific medicine, experiments provided a means of artificially creating a diseased condition. Thus, the programmatic statements of Henle, Virchow, and others stressed the use of physiological experiments, pathological anatomy, microscopy, chemistry, and clinical observation as the tools for analyzing bodily functions and how they become diseased. While sympathetic to the goals of Henle and Virchow, Helmholtz, du Bois-Reymond, and Briicke focused not on the reform of medicine but rather on the means for establishing an autonomous physiological science. In particular, they wanted to transform physiology into an "organic physics." In 1847 the three friends, along with Karl Ludwig, took an oath to reduce physiology to its chemical and physical foundations, creating an "organic physics" based exclusively upon mathematical, physical, and chemical laws.1sIn developing this new approach "the 1847 group" (as Paul Cranefield has labelled them) relied heavily upon sophisticated instruments and instrumental techniques. Du Bois-Reymond's astatic galvanometer and induction apparatus, Helmholtz's myograph, ophthalmoscope, and ophthalmometer, and Ludwig's kymograph and vacuum pump illustrate a few of the many instruments conceived of and in part constructed by this new generation of physiologists.19 These instruments simplified the conditions for experimenting on isolated organs, allowed better control of phenomena, aided in the establishment of causal connections, and permitted exact measurements and graphical representation of organic functions. They required, moreover, a level of mathematical 17. Claudia Huerkamp, Der Aufitieg der k'rzte i m 19. Jahrhundert (Gottingen: Vandenhoeck und Ruprecht, 1985); E. Ackerknecht, "Beitrage zur Geschichte der Medizinalreform von 1848," Sudhoffs Archiv 25 (1 932):61-109, 1 13-83; and Arleen Tuchman, Science. Medicine, and /he State in Germany: The Case o f Baden. 1815-1871 (Oxford and New York: Oxford University Press, 1993). 18. Paul Cranefield, "The Organic Physics of 1847 and the Biophysics of Today," JfJMAS 12 (1957):407-23. 19. K.E. Rothschuh, "Emil Heinrich du Bois-Reymond," DSB 4 ( 1 971):200-5; Heinz Schroer, Carl Ludwig. Begriinder der messenden E.xperimmtalphysiologie (Stuttgart: Wissenschaftliche Verlagsgesellschaft, 1967), 104-14, 170-80; Stanley Joel Reiser, Medicrneand the Reign of Technology (Cambridge and London: Cambridge University Press, 1978), 100- I; and below, Section 3.

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skill and technical dexterity that clearly distinguished the methodological approach of the "organic physicists" from the microscopical, chemical, and vivisectional skills of individuals like Henle and Virchow. Despite Helmholtz's commitment to the transformation of physiology into an exact science, he could not devote his energy solely to this pursuit. In late September 1842, having completed his course work at the Institut, he began his year-long medical "internship" in the Charit&,an experience he found both difficult and ~ h a l l e n g i n gHis .~~ first assignment in the ward for internal diseases proved to be his most demanding. He began each day at seven o'clock, examining his own patients before malung the rounds with his supervisor and other interns, at which time he reported on his findings and suggested appropriate therapeutic measures. The entire procedure lasted over four hours and occurred twice daily. During the remaining hours, he performed autopsies and recorded the daily events in the hospital journal. His day did not end until eight o'clock in the evening2' Helmholtz's most difficult months were the first two, when his immediate supervisor proved to be a tyrant and most of his patients suffered from chronic illnesses for which he could do little more than prescribe opium. Although he welcomed the opportunity to study these illnesses firsthand, he was relieved when rotations toward the end of the year placed him in a ward with more varied cases and a supervisor who permitted the interns greater responsibility for their patients. He found this work more rewarding-not only did he come into contact with "a selection of the most interesting patients"; he also found time to further his medical knowledge by visiting Schonlein's clinic, "in which one receives multiple stimulations to a deeper understanding of the disease He clearly enjoyed his work in the Charite, his only disappointment being that he had so little time to conduct his own research. During the fall of 1842 he managed only to put the finishing touches on his dissertation, which he defended on 2 November 1842. Entitled De fabrica svstematis nervosi evertebratorum ("The Structure of the Nervous System in Invertebrates"), the thesis went beyond Helmholtz's initial study by demonstrating the link between 20. Helmholtz's attitude toward his internship is revealed in several letters to his parents: 7 October, 8 December, and 19 December 1842, and 16 January and 8 February 1843, in Cahan, ed., Letters, 92-3, 95-6, 96-7. 98-9, 99-100, resp. 2 1. Helmholtz to his parents, 7 October 1842, in ibid., 92-3. Rudolf Virchow's experience as an intern in the Charit6 was similar to Helmholtz's. See Virchow's letter to his father of 14 May 1843, in Marie Rabl, ed., Rudolf L'irchow. Briefe an seine Eltern 1839 his 1864 (Leipzig: W . Engelmann. 1907), 64. 22. Helmholtz to his parents, 16 January 1843, in Cahan, ed., Letters. 98-9.

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ganglionic cells and nerve fibers in a host of organisms, both invertebrate and ~ e r t e b r a t e . ~ ~ Beginning in February 1843, Helmholtz was able to allot more time to his scientific studies. Having completed his tour of duty in internal medicine, he moved on to the children's ward, followed by obstetrics, where there was little to do.24He took advantage of this situation by spending more time in Miiller's laboratory, where he conducted experiments on putrefaction and fermentation, a topic he viewed as fertile ground fo: furthering the goal of the "organic physicists." At the time, scientists disagreed as to whether these processes were essentially chemical or dependent upon the presence of living organisms. Helmholtz's experimental results, probably to his dismay, were equivocal.25 Although they seemed to demonstrate that putrefaction involved a process of decay that occurred independently of any life forms, they also indicated that fermentation, although a form of putrefaction, resulted only when a living organism was introduced to the putrifying medium. Thus Helmholtz had not succeeded in reducing all organic processes to their chemical and physical components. Helmholtz's clinical internship ended on 1 October 1843, at which time he was promoted to staff surgeon to the Royal Hussars at Potsdam and transferred to an army hospital there.26He remained in his native city for the next five years, dividing his time between his medical responsibilities and scientific research. The former were not overly demanding. Helmholtz managed to establish a small laboratory in the army barracks so as to conduct experiments. During his Potsdam years (1 843-48) he shifted his focus of research from putrefaction and fermentation to the source of heat production during muscle contraction, conducting experiments that led ultimately to his articulation of the principle of the conservation of force. He now recognized that the ability to explain animal heat as a function of the chemical transformations occurring within the muscles was better suited for his plans to create an "organic physics." Between 1843 and 1847 he showed experimentally that chemical changes occur in the muscle tissues during activity; that heat emission accompanies this process; and that this heat is not brought to the muscles by the nerves or blood but rather is produced in the tissues themselves. Having demonstrated these 23. De Fahrica. 24. Helmholtz to his parents, 8 February 1843, in Cahan, ed., Lellers, 99-100. 25. "Ueber das Wesen der Faulniss und Gahrunn." MA (I 843):453-62, in WA 272634. For discussion of this work see the essay by Kathryn M. 0lesko and Frederic L. Holmes, "Experiment, Quantification, and Discovery: Helmholtz's Early Physiological Researchs, 1843-50," in this volume. 26. Koenigsberger 1:54.

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chemical physiological facts, he then analyzed and quantified this physiological process, deriving a mechanical equivalent for the amount of heat produced. This work formed an important part of his monograph, Ueber die Erhaltung der Kraft, which he published in 1847.*' By establishing the principle of the conservation of force, Helmholtz had effectively demonstrated the superfluousness of evoking any special life forces as explanatory principles. Although Helmholtz's work on the conservation of force received a mixed review, there could be no doubt that he was a man of much promise. Apart from Muller's support, he now won that of the influential Alexander von Humboldt, who always had a keen eye for talented young scientists. When Briicke, who had been teaching anatomy at the Akademie der Kunste in Berlin, received a call to Konigsberg as extraordinary (auflerordentlicher) professor of physiology and pathology, von Humboldt arranged to have Helmholtz released from his military duties so that he could succeed B r i i ~ k e Thus, . ~ ~ three years before the projected completion of his official military obligations, Helmholtz entered into a civilian, academic career. Although Helmholtz never again practiced medicine after he left the army in 1848, his ties to the medical community remained unbroken. This connection manifested itself first and foremost institutionally: until he moved to Berlin in 1871 as professor of experimental physics, he taught in medical faculties, even lecturing on pathology during the six years he spent in Konigsberg (1 849-55). This medical connection, however, extended well beyond an institutional affiliation. In his work, particularly in physiological optics, Helmholtz made several significant contributions to the medical world. The most important of these was his invention of the ophthalmoscope, an instrument which, more than any of his other discoveries, made his reputation in the medical community and beyond. It was, as he later said, "the most popular of my scientific achievement^."^^ Indeed, it was the invention that launched him on his stupendously successful career. Its invention and the medical community's response to it are the focus of Section 3. 27. Ueber die Erhaltung der Kraft (Berlin: G. Reimer, 1847). Helmholtz's experiments between 1843 and 1847 are published in "Ueber den Stoffverbrauch bei der Muskelaktion," MA (1845):72-83; and in "Ueber die Warmeentwicklung bei der Muskelaction," ibid. (1848):144-64, both in WA 2:735-44 and 745-63, respectively. On his principle of the conservation of force see Fabio Bevilacqua's essay. "Helmholtz's Ueber die Erhaltung der Kraft: The Emergence of a Theoretical Physicist." in this volume. 28. Koenigsberger 1:93-110. 29. "Erinnerungen," in I'R' 1: 12.

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3. Helmholtz's Ophthalmoscope: Its Invention and the German Medical Community's Response Helmholtz remained at the Akademie der Kunste for only one year. In the summer of 1849 Brucke transferred to Vienna as professor of anatomy and physiology, and his position in Konigsberg went to Helmholtz. In his new capacity as extraordinary professor in the medical faculty, Helmholtz had responsibility for teaching not only physiology but pathology as well. He held this position for the next six years (1 84955). During his Konigsberg years, Helmholtz continued his studies of nerve physiology (measuring the velocity of the nerve impulse), and also moved on to physiological optics and acoustics-two areas that occupied his attention for nearly twenty years.30His interests continued to center on the physical foundations of sensory stimulation and the epistemological foundations of sense perception; yet while preparing a lecture on optics for his medical students, Helmholtz realized that certain rather simple laws of geometrical optics permitted him to construct an instrument of potentially great diagnostic importance to the medical community-the ophthalmo~cope.~~ 30. "Messungen iiber den zeitlichen Verlaufder Zuckung animalischer Muskeln und die Fortpflanzungsgeschwindigkeit der Reizung in den Nerven," MA (1850):276-364; "Messungen iiber Fortpflanzungsgeschwindigkeit der Reizung in den Newen. Zweite Reihe," ibid. (1852): 199-216, both in W 2:764-843 and 844-6 1, respectively; Handbuch; and Die Lehre von den Tonempfindungen als physiologische Grundlagejiir dre Theorre der Musik (Braunschweig: F. Vieweg and Sohn, 1863). For analyses of Helmholtz's work in these areas see the respective essays in this volume by OIesko and Holmes. "Experiment. Quantification. and Discovery"; R. Steven Turner, "Consensus and Controversy: Helmholtz on the Visual Perception of Space"; Richard L. Kremer, "Innovation through Synthesis: Helmholtz and Color Research"; and Stephan Vogel, "Sensation of Tone, Perception of Sound, and Empiricism: Helmholtz's Physiological Acoustics." 3 1. Beschreibung eines Augen-Spiegels zur Llnrersuchung der Netzhaut Im lehenden ifuge (Berlin: A. Forstner, 1851). On Helmholtz's invention of the ophthalmoscope see, for example, Richard Greef, "Historisches zur Erfindung des Augenspiegels," Berlrner klinrsche Ubchenschrifi 38:48 (I 90 I ): 1201-2; Koenigsberger I: 133-43; Ernest Engelking, ed., Dokurnente zur Erjndung des Augenspiegels durch Hermann von flelmholtz irn Jahre 1850 (Munich: J.F. Bergmann, 1950); Albert Esser, "Zur Geschichte der Erfindung des Augenspiegels," Klinische Monatsblatter,fur Augenheilkunde 116 (1 950): 1- 14; Wolfgang Jaeger, ed., Die Erfindung der Ophthalrnoskopie dargestellt in den Originalheschreibungen der dugenspiegel von Helmholfz. Ruere und Giraud-Teulon (Heidelberg: Brausdruck, n.d. [1977]); Reiser. Medicine and the Reign of Technology, 46-8; Klaus KlauB, "Ein neuentdecktes friihes Dokument zur Geschichte der Erfindung des Augenspiegels durch Herrnann v. Helmholtz," NTM 18:1(1981):58-61; George Gorin, ffistory yfOphthalmolog~~(Wilrnington, Del.: Publish or Perish. 1982). 129: and Frank W. Law. "The Origin of the Ophthalmoscope." Ophthalmology 93:I ( 1986):140-4 1 .

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Helmholtz wanted to describe the phenomenon, observed by both William Cummings, an English physician, and Briicke, wherein the human eye glowed in a dark room when light was directed at the eye and an observer stood near the light source. Neither Cummings nor Briicke had managed to see the eye's inner structure; whenever they approached the eye closely enough to peer inside it, the glare from the light source diffused over the entire pupil. While preparing his lecture, Helmholtz asked himself how the light rays reflected back from the illuminated eye produce an optical image; he was thus led to analyze the rays' paths. He discovered that the rays followed an identical path when entering and leaving the eye; this allowed him to explain Briicke's inability to see the internal structure: to do so Briicke would have had to stand directly in the path of the light rays, thus blocking the light source. It took Helmholtz merely eight days to circumvent the problem and invent an instrument that permitted him to see the retina and vessels within the living eye. He used a plane-polished glass surface which both reflects and transmits light, and thus acts as a partial mirror. By looking through this glass, which he placed at an angle, and using one surface to reflect light into the observed eye, he was able to eliminate the glare while allowing enough light to return so as to permit a clear view of the retina. Figure 1.1 presents Helmholtz's own schematic arrangement of the ophthalmoscope and ray paths. Here C is the planepolished glass. A candle A illuminates the glass plate, whereby most of the light is reflected into the eye D being observed. The dorsal area of the eye (i.e., the retina) in turn reflects this light back along the same path by which the rays had entered. Some light returns to A while some continues in a straight line (the reverse path of entry) through the glass plate and on to the eye of the observer G. Since the latter must stand very close to the person being observed in order to see through the pupil's small opening, the light rays entering the observer's eye converge, resulting in a blurred picture. To circumvent this problem, Helmholtz placed a concave lens F between the observer and the glass plate. His ophthalmoscope, at least in its initial, highly primitive form, was complete. In December 1850 Helmholtz wrote his father expressing his surprise that no one before him had figured out how to construct such an i n ~ t r u m e n tHe . ~ ~reported that he had needed only the most elementary knowledge of optics. Indeed, he had actually worked out some of the optical laws while still a student at the Potsdam Gymnasium. 32. Koenigsberger 1:133-34.

Figure 1.1. Schematic drawing of the path taken by light as it travels through the ophthalmoscope. Source: Beschreibung eines Augen-Spiegels zur Untersuchung der Netzhaut im lebenden Auge (Berlin: A. Forstner, 1851), 47; reprinted in Klassiker der Medizin (Leipzig: J.A. Barth, 1910). 12.

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Yet he underestimated the mathematical knowledge needed to comprehend the geometrical optics upon which the ophthalmoscope was based. Some of the physicians who voiced opposition toward the instrument (about which more presently) may have done so because of their inability to understand the physical and mathematical principles involved in the instrument's construction. Yet Helmholtz's geometrical knowledge did not alone lead to the idea of the ophthalmoscope. As he himself later noted, his success resulted from his hybrid education: he knew more physics than physicians, and more physiology and medicine than physicists and mathematician~.'~ His medical studies had familiarized him with the practical problems confronting ophthalmologists, leading him to recognize the diagnostic potential of an instrument that would permit physicians to investigate changes in the retina. He was aware, moreover, of recent developments in medical diagnostics which had begun to free physicians from their dependence upon gross physical symptoms and patients' own accounts of their ailments. Of particular importance here were new types of analyses and techniques, such as physical diagnosis, pathological anatomy, and microscopy, which seemed to provide physicians with more objective information about the internal organic changes accompanying the diseased state (although the interpretation of this information often remained disputed). No instrument better exemplified this transition than the stethoscope, which was invented in the early nineteenth century and which made audible what was invisible to the physician's gaze.34 Helmholtz realized immediately that an ophthalmoscope would similarly reveal what had previously remained hidden-the anatomical and physiological changes of the eye's interior. He wrote to his father: Until now a series of the most important eye diseases, included under the name "black cataract," have been terra incognita because one could

learn nothing about the changes in the eye either in the living [state] or even after death. My invention will make possible the finest investigation of the internal structures of the eye. . . . Where possible, I shall examine patients with the chief ophthalmologist here and then publish the material.I5 Helmholtz published the results of his work in 1851 in a small pamphlet entitled Beschreibung eines Augen-Spiegels zur Untersuchung der 33. "Erinnerungen," VR' 1:13. 34. Reiser, Medicine and the Reign of Technology, chap. 2; and Michel Foucault, The Blrth of the Clinic (New York: Vintage Books, 1973). 35. Koenigsberger 3: 142f.

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Netzhaut im lebenden Auge. The medical community responded immediately. Among general practitioners, particularly older ones, some voiced opposition to the instrument. Helmholtz reported that one colleague condemned the ophthalmoscope as a dangerous instrument for letting too much light into the eye. Indeed, one of the loudest objections was that prolonged exposure of the retina to light could lead to blindness; some critics thus charged that the ophthalmoscope actually created diseases. Other complaints stemmed from difficulties in understanding and using the instrument. One of Helmholtz's colleagues reportedly went so far as to claim that only those with poor eyesight needed the assistance of such an in~trument.'~ These hostile responses aside, the ophthalmoscope received extensive positive publicity in scientific and medical journals soon after its invention. Although general practitioners probably did not use the ophthalmoscope in their routine patient examinations until the end of the century, it appealed immediately to a sizable group of physicians with specialist interests in optometry and ophthalmology. By early December 1851 Helmholtz had received eighteen orders for his instrument. Between 1851 and 1856 at least sixteen books and eighteen articles were written on the ophthalmoscope. Several of these books aimed specifically at teaching physicians how to use the instrument: for example, Der Augenspiegel und das Optometerfurpraktische Aerzte (1852), by Christian Georg Theodor Ruete, extraordinary professor of ophthalmology at the University of Gottingen; and Ueber die Anwendung des Augenspiegels, nebst Angabe eines neuen Instruments (1 853), by Ernst Adolf Coccuis, Privatdozent in ophthalmology at the University of Leipzig.)' These specialists felt deeply indebted to Helmholtz and his instrument for their own recent successes. In 1854, for example, in a review of Helmholtz's work in the Medicinische Centralzeitung, one author adopted an ecstatic tone, characterizing Helmholtz as the . ~ ~ in "emancipator and liberator" of the field of o p h t h a l m ~ l o g yAnd the same year, Albrecht von Graefe, then a practicing ophthalmologist in Berlin and lecturer at the university, founded a specialist journal, Archiv fur Ophthalmologie, in which he attributed the field's great upswing to Helmholtz's i n ~ e n t i o n . ' ~

36. "Das Denken in der Medizin," VR3 2179. For other discussions of opposition to the ophthalmoscope, see Reiser, Medicineandthe Reign of Technology, 50; and Gorin, Ifistorj~of Ophthalmolog.y, 129. 37. These and other works are listed in F. Heymann, "Die Augenspiegel, ihre Construktion und Verwendung," Schmidt k Jahrbiicher der In- und Auslandischen gesammten Medicin 89 (1856): 105-22. 38. Medicinische Cenfralzeitung, 1 November 1854, noted in Mitfheilungen des hadirchen arztlich~nVereins 9 (1855):last page (no pagination). 39. Albrecht von Graefe, "Vonvort," .4O I ( 1 854):~-x.

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The ophthalmoscope revolutionized the study of eye disease. Von Graefe, hailed as one of the founders of modern ophthalmology, praised the instrument for "revealing to us a new world," and for allowing the investigation of what had previously remained opaquethe various anatomical, physiological, and pathological changes of the inner eye.40The terra incognita, for example, to which Helmholtz had referred-black cataract-lost much of its mystery. The condition represents an advanced cataract state in which sclerosis causes the lens to change color, eventually turning a very dark brown, if not black. It was a condition, one ophthalmologist claimed, in which "the patient sees nothing, but neither does the p h y ~ i c i a n . " ~Ophthal~ moscopic investigations permitted early diagnosis of the disease and made it easier to distinguish between cataracts and other eye disorders, such as amblyopia, which are also marked by the gradual loss of sight. Most importantly, increased knowledge of cataracts led to therapeutic advances. In 1865 von Graefe improved upon the standard procedure for removing cataracts, which had involved a corneal flap incision, by substituting a linear incision in the sclera. This technique significantly reduced the morbidity associated with cataract Cataract victims were neither the first nor the only individuals to benefit from the ophthalmoscope. As early as 1856 von Graefe performed the first successful iridectomy for acute glauc0ma.~3He removed a portion of the iris in order to reduce the ocular tension responsible for the discomfort and blindness associated with the disease. The ophthalmoscope helped von Graefe develop this therapeutic technique by allowing him to ascertain definitively that glaucoma arose not, as some had claimed, from changes in the optic nerve, but rather from increased intraocular pressure. Experiments with alternative procedures for reducing this pressure eventually led him to consider and develop the technique of iridectomy. In addition to aiding the development of surgical techniques, the ophthalmoscope also advanced the study of optic pathology. Within a decade of the instrument's invention, ophthalmologists identified and described thrombosis and embolies of the retinal arteries, pigmentary retinitis, retinal detachment, and degenerative diseases of 40. Quoted in Eduard Michaelis, Albrecht von Graefe. Sein Leben und Wirken (Berlin: G. Reimer, 1877), 39. 4 1. Greef, "Historisches zur Erfindung des Augenspiegels," 1201. 42. George E. Amngton, Jr., A History ofOphthalmology (New York: MD Publications, Inc., 1959), 93. 43. Albrecht von Graefe, "Ueber die Iredectomie bei Glaucorn und iiber den glaucornatomsen Process," A 0 3:2 (1 857):456-560.

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the retina.44 Furthermore, they explored pathological conditions of the eye associated with general systemic diseases. Richard Greeff, professor of ophthalmology at Berlin around the turn of the century, viewed the inner eye as an ideal window to other bodily diseases because alterations in the fine structures of the retina often reflected pathological changes elsewhere in the body. To support this claim, he cited a host of discoveries made within a decade of the ophthalmoscope's invention, including retinal changes associated with diabetes mellitus, leukemia, syphilis, and diseases of the brain and kidneys.45 If the ophthalmoscope was Helmholtz's most important contribution to the medical community, it was certainly not the only one. He also did important work on accommodation-the process by which the eye adjusts its focus to maintain a clear picture of objects at different distances. Prior to his work in 1856 on accommodation, there existed several contradictory theories about the process of accommodation. Some claimed accommodation occurred through contraction of the pupil; others that it depended on changes in either the curvature of the cornea, the shape of the eyeball, the position of the lens, or the shape of the lens. To test these competing theories, Helmholtz invented an instrument-the ophthalmometer-that permitted him to measure changes in the curvature of the cornea and in the anterior and posterior surfaces of the lens. Most importantly, the ophthalmometer permitted these measurements in the living eye. Helmholtz found that changes in the shape of the lens alone account for accommodation, and he described how the anterior surface of the lens became more convex, the apex moved forward, and the axial portion grew thicker when the eye focused on objects nearby. When objects were far away, the reverse occurred. He postulated, moreover, that tension and relaxation of the ciliary muscles were primarily responsible for the changes in the shape of the lens.46 Helmholtz published his results in 1856 in von Graefe's Archiv fur Ophthalmologie. Aware of the journal's medical readership, he closed

44. Wolfgang Miinchow, Geschichte der Augenheilkunde (Stuttgart: Ferdinand Enke Verlag, 1984), 584; and Gorin, History of Ophthalmology, 132-39. The individuals most responsible for this work included Coccius, Frans Cornelis Donders, Albrecht von Graefe, Julius Jacobson, Eduard Jaeger, Hermann Jakob Knapp, Richard Liebreich, and Ruete. 45. GreefT, "Historisches zur Erfindung des Augenspiegels," 1201 ; and Miinchow, Geschichte der Aug~nheilkunde,584. 46. "Ueber die Accommodation des Auges," A 0 2 (1856):l-74, in WA 2283-345. See also Handhuch 1:103-25; and "Die neueren Fortschritte in der Theorie des Sehens ( 1 868)," in VR' 1:233-331 (Helmholtz discusses the ophthalmometer on 243).

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Physiologist

his article on accommodation with a discussion of the medical significance of his work. His theory, he noted, offered a reasonable explanation of the fact, well known to clinicians, that people with severe mydriasis (enlargement of the pupil) or iridectomies still retain some ability to accommodate. Helmholtz, who knew that greater knowledge of these diseased conditions would assist him in his work, appealed to ophthalmologists to carry out research "in the interests of the physiological theory of accommodation, and determine exactly the power of accommodation of these eyes."47Moreover, he encouraged several of his advanced students to pursue clinical studies in ophthalmometry. One in particular, Hermann Jakob Knapp, applied the ophthalmometer to studies of the curvature of the human cornea, confirming Helmholtz's claim that accommodation occurred through changes in the lens and not the cornea.4ROther individuals, above all Franciscus Cornelis Donders, one of Europe's leading ophthalmologists and co-editor of Graefe's Archiv, soon used the ophthalmometer to study common eye disorders. Donders worked out exact determinations for nearsightedness, farsightedness, and for astigmatic conditions, in which irregularities in the curvature of the cornea create optical distortion^.^^ Helmholtz's work in physiological optics thus made an indisputable impact on medical practice. He appreciated this and cultivated his medical connections wherever possible. It was, for example, to the Konigsberg Gesellschaft fiir wissenschaftliche Medizin, which had elected him president in 1850, that he first presented the ophthalmoscope. Shortly thereafter, while touring physiological institutes in Germany, he contacted members of the scientific and medical communities in order to demonstrate his instrument. The ophthalmologist Ruete, whom Helmholtz first met in Gottingen, was particularly pleased with what he saw. "For my trip," Helmholtz wrote his wife, "the ophthalmoscope has been splendid. I demonstrated it this rnorning and created a sensation here as well."50 Indeed, whenever Helmholtz's research led him to a discovery of potential medical significance, such as his work on accommodation, 47. "Ueber die Accommodation des Auges," in WA 2:345. 48. Hermann Jakob Knapp, "Uber die Lage und Knimrnung der Oberflachen der menschlichen Kristallinse und den Einfluss ihrer Veranderungen bei der Akkommodation auf die Dioptrik des Auges," A 0 6:2 (1860): 1-52; 7:2 (1860): 136-38. On Knapp, see Blographisches Lexikon der hervorragenden Arzte aller Zeiten und Volker, 2nd ed., 5 vols. (Berlin and Vienna: Urban and Schwarzenberg, 1928-34), S.V."Knapp, Hermann Jakob." 49. "Die neueren Fortschritte," I'R3 1:243-44. 50. Helmholtz to his wife Olga, 6 August 185 1. in Richard L. Krerner, ed., Letrers of Hermann yon Helmholtz to Hls U'('fe 1847-1859 (Stuttgart: Franz Steiner Verlag. 1990), 51.

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he advertised it to the medical community. In 1852, moreover, he simplified the ophthalmoscope's external fittings, and published his results in Karl Vierordt's Archiv furphysiologische Heilkunde, a journal that reached a wide medical audiences' Yet nowhere was Helmholtz's interest in publicizing the medical significance of his work more obvious than in his Handbuch der physiologischen Optik, the first volume of which appeared in 1856. In 1854 he told his friend Adolph Fick, Privatdozent for physiology at the University of Zurich, that although he had decided against writing the Handbuch in a popular fashion for physicians, he did arrange it so that everything of medical significance was grouped together.52Thus, physicians, uninterested and usually unqualified to understand the mathematical parts of Helmholtz's text, could easily focus on the sections which included an encyclopedic presentation of the anatomy of the eye, its dioptric, its various imperfections resulting in nearsightedness, farsightedness, and astigmatism, as well as a description of the ophthalmoscope and ophthalmometer. Helmholtz's success in reaching the medical community led several ophthalmologists to hail the Handbuch as their bible, the foundation text for the newly emerging science of ~phthalmology.~~ Helmholtz's interest in encouraging close ties to the medical community derived from his appreciation of how physicians and physiologists could mutually benefit each other.54Concerning the contributions physiologists made to medicine, he could point to his own invention of the ophthalmoscope or to Ludwig's invention of the kymograph, which permitted the graphical representation of physiological processes, such as respiration and blood pressure changes.55But more important to physicians, experimental physiology exemplified the proper methodological approach to the study of organic processeswhether healthy or diseased. As one physician wrote in the Mittheilungen des badenischen arztlichen Vereins in 1852, the student who learned the exact method in the physiological laboratory had "so cultivated his sense for the proper way of looking at things . . . that the only task left would be to give instruction on how to direct his experience through the great labyrinth of pathology and therapy."56 5 1. "Ueber eine neue einfachste Form des Augenspiegels," Vierordt's Archivfur Physiologische Heilkunde I 1 ( 1 852):827-52, in WA 2:261-79. 52. Koenigsbcrger 1:265. 53. Noted in Greeff, "Historisches zur Erfindung des Augenspiegels," 1202. 54. Cf. Timothy Lenoir's essay, "The Eye as Mathematician: Clinical Practice, Instrumentation, and Helmholtz's Construction of an Empiricist Theory of Vision," in this volurnc. 55. On Ludwig's invention of the kymograph see Reiser. Medicine and the Reign of fi~hnology,100- 1. 56. Anon., "Wie sollen die Aerzte gebildet werden?," Mittheilungen des hadischeti arzilirhan L'ereitzs Y (12 May 1852):65-9, quote on 66.

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Physiologist

Helmholtz shared this conviction. He believed that the method medical students learned in the laboratory provided them with the necessary mental outlook for making accurate prognoses. The physician, he explained, must strive to know in advance what the result of his intervention will be if he proceeds in one way or the other. In order to determine in advance what has not yet happened or what has not yet been observed to happen, there is no other method than to learn through observation the laws governing phenomena; and these can be learned through induction-through the careful search, production, and observation of those cases which fall under the law.57 The proof of these claims for Helmholtz rested in the improvements medicine had already accrued through the adoption of the experimental method, including advances in microscopy, pathological anatomy, and physiology. But he believed no branch of medicine demonstrated his point more clearly than ophthalmology. In a popular lecture delivered in 1869 entitled, "Ueber das Ziel und die Fortschritte der Naturwissenschaften" ("On the Aim and Progress of Natural Science"), he reminded his audience that correct knowledge of the structure and composition of the eye, acquired through the inductive method, had permitted the construction of corrective lenses, as well as the early diagnosis and treatment of diseases which had previously resulted in blindness. For Helmholtz, ophthalmology had become for the other branches of medicine "as brilliant an example of the capabilities of the true method as astronomy had long been for the other science^.''^^ If the medical community benefited from physiology, the reverse was also true. For one, medical research occasionally provided valuable information on normal bodily functions, as in Charles Bell's experimental work of 181 1 in which he demonstrated the functional specificity of the peripheral nerves of the brain. Bell had derived his idea from exact observations at the bedside, leading one clinician to predict that "it may easily happen that more light will come to the theory of the movement of the heart through pathological observations by means of the stethoscope than through all the physiological experiments done to date."59Moreover, physiologists occasionally received confirmation 57. "Das Denken in der Medizin," VRJ 2: 183. 58. "Ueber das Ziel und die Fortschritte der Naturwissenschaften," in VR3 1:33363, on 362. 59. Carl Pfeufer, "Ueber den gegenwartigen Zustand der Medizin. Rede gehalten bei dem Antritt des klinischen Lehramts in Ziirich den 7 November 1840," Annalen der

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of the validity of their theories from physicians engaged in clinical research, as in Knapp's validation of Helmholtz's theory of accommodation. Finally, physiologists turned to the medical community for assistance in their struggle for disciplinary autonomy. Several members of the 1847 group had appreciated the help physicians could offer them in their fight to win institutional support in the university medical faculties. Early in his career Ludwig, for example, initiated a steady correspondence with Henle, then professor of anatomy, physiology, and pathology at the University of Heidelberg. Henle, who directed his work toward the elimination of boundaries between physiology and pathology, had strong ties to the medical community. When Ludwig first contacted him in 1846, Henle was already co-editor, together with the clinician Karl Pfeufer, of the Zeitschrift fur rationelle Medizin, a journal dedicated to convincing physicians of the necessity of founding medicine upon a physiological basis. Ludwig believed Henle was ideally positioned to help him persuade physicians of the relevance of experimental research for medicine. "It has become obvious to me," he wrote in his first letter to Henle, "that we calculators and experimentalists would not be able to live at all without a person like you."60 Like Ludwig, Helmholtz was also aware of the advantages that support from the medical community could offer the experimental physiologists. He admonished his friend du Bois-Keymond, whose research concentrated almost exclusively on nerve physiology, to keep this concern in mind. Indeed, he believed du Bois-Reymond's difficulties in the 1850s in landing an appointment as professor of physiology issued from his apparent indifference toward the medical community. "You can well imagine," he wrote his friend, that men of practice lash out here and there at your lecturing style in physiology. . . . 1 will leave it to you to judge whether it is worth your while to further reduce the time you spend on animal electricity in physiology in order to acquire a better opinion from the [medical] f a ~ u l t y . ~ '

Helmholtz's advice to du Bois-Reymond stemmed from his own positive experience. Six years had passed since he had invented the ophthalmoscope and earned a reputation in medical circles. The ophthalmoscope, he knew, had in many ways made his career. "For stadtischen allgernein~nKrankenhauser in Munchen I ( I 878):395-406, quote on 4045. 60. Ludwig to Henle, 19 July 1846 and 27 March 1849, in Astrid Dreher, Briefe von Carl Ludwig an Jacob Henle aus den Jahren 1846-1872 (Med. diss. Heidelberg. 1980). 43-5 and 67-72, respectively, quote on 44. 61. Helmholtz to du Bois-Reymond. 26 May 1857, in Kirsten, 171-73, on 172.

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my place in the world," he later wrote, "the construction ofthe ophthalmoscope was very decisive. Among authorities and colleagues, I found, thereafter, such an appreciation of and benevolence toward my requests, that I was able to pursue the inner drive of my intellectual curiosity much more easily."62 Helmholtz's favorable reputation in medical circles permitted him to define his research projects as he wished, and even to move slowly away from teaching routine medical courses. This became evident in 1855 when he expressed interest in leaving Konigsberg for a position as professor of anatomy and physiology in Bonn. He wanted to move for personal and professional reasons: he was concerned about the adverse effects of the cold northern Prussian winters on his wife's health and believed that Bonn would provide milder weather; he expected to have more influence on the scientific community from Bonn than from Konigsberg; he wanted a slightly higher salary; and he wanted to redefine his teaching responsibilities so as to exclude pat h ~ l o g y . As ~ ' he wrote in 1854 to Johannes Schulze, the Prussian minister of cultural affairs, he no longer felt fully capable of or interested in representing this subject: It has been m y wish for a long t i m e t o b e able t o substitute general pathology, o n which I lecture here, with anatomy, because the latter lies m o r e within m y interests t h a n t h e former. I sense m o r e a n d m o r e by the questions a n d viewpoints that h a v e recently arisen i n pathology that t h e notions that I acquired during m y earlier medical practice a r e n o longer totally sufficient, a n d I m u s t fear that this will grow worse every year.64

Helmholtz got his wish, and in 1855 he moved to Bonn. This move marked his first step away from the teaching of medical subjects proper. However, from the moment he anived in Bonn he had problems with the research and teaching facilities. The anatomical institute, he wrote du Bois-Reymond, "is in a gruesome condition. Physiological instruments are few, and [Julius] Budge [the professor of physiology] has let these perish in dirt."65 The situation was so bad that he had to set up 61. Helmholtz to du Bois-Reymond, 26 May 1857, in Kirsten, 171-73, on 172. 62. "Erinnerungen," VR5 1:12-3. 63. See Helmholtz to du Bois-Reymond, 5 November 1854, and to Johannes Schulze, 3 and 19 December 1854, and Alexander von Humboldt to Johannes Schulze, 24 March 1855, and to Helmholtz, 24 March 1855, in Koenigsberger 1:225-31, 248-51. 64. Helmholtz to Schulze, 19 December 1854, quoted in ibid., 1:230-31. 65. Helmholtz to du Bois-Reymond, 14 October 1855, in Kirsten, 157. For a discussion of Helmholtz's problems at the University of Bonn see Tuchman, Science, Mehrrne, and the State, chap. 7.

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41

a laboratory at home in order to conduct experiments. For three years he fought with the Bonn administration and the Prussian ministry to get funds to purchase instruments and to finance a new institute for anatomy and physiology. Several times he almost succeeded, yet each time something delayed funding appropriation. To make matters worse, he began to be blamed for the atrocious state of Bonn's institutional f a ~ i l i t i e sFrustrated .~~ and disgusted, he decided to leave Prussia in 1858 for the University of Heidelberg in Baden. Heidelberg offered him not only a newly created chair in experimental physiology and a salary of 3,600 gulden (which was the highest salary paid at the university), but promised him a brand new physiological institute equipped with workspace for himself and students, and a substantial yearly endowment to pay for supplies and instruments for both his His appointment and the motives behind teaching and his ~esearch.~' Heidelberg's generosity fell within the larger context of medical reform in Baden during the 1850s.

4. Medical Reform in Baden and the Search for an Experimental Physiologist Baden's decision to invest heavily in experimental physiology was closely tied to broader interests in medical reform. In 1858, the very same year in which Helmholtz was hired, the government totally revamped its state medical examination and licensing requirements. The benefits which Helmholtz anticipated through involvement in the medical community continued to accrue. Yet experimental physiologists were not the only beneficiaries of this connection. Medical reformers perceived an advantage to themselves as well. In their attempt to turn medicine into a science, they stressed the importance of incorporating the exact method of the experimental sciences into medical education and research. They believed that by learning this method in the laboratory, students would acquire an analytical tool that they could later apply at the bedside. Thus the institutionalization of the experimental sciences at the University of Heidelberg (and at other 66. Helmholtz discusses the deplorable conditions in Bonn in a letter to Justus Olshausen, 16 April 1858, Darmstaedter Collection, File F I a 1847: Hermann von Helmholtz, Staatsbibliothek PreuDischer Kulturbesitz, Berlin, Handschriftenabteilung. 67. The negotiations surrounding Helmholtz's appointment as professor of physiology in Heidelberg are discussed in Rep. 235129872, Badisches Archiv. On his salary being the highest in the university see the report from the Ministerium des lnnern to the Staatsministerium. 17 February 1858, ibid.

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universities as well) reflected a broader-based conviction that training in the experimental method would ultimately translate into practical benefits. Interest in medical reform in Baden dated back to the 1840s, when university-trained physicians throughout Germany united to fight for the standardization of stricter educational and licensing requirements. They sought to convince state governments to grant them a monopoly over health care; yet at the time they could hardly claim greater effectiveness than their competitors. By arguing for stricter educational requirements, physicians were promising to acquire those skills that would make them superior to their competitors; and they saw increased training in the natural sciences, particularly in the laboratory and clinic, as a means of acquiring that s u p e r i ~ r i t y . ~ ~ In 1848, during the height of the medical reform movement and one year after Helmholtz and his friends took their oath to transform physiology into an "organic physics," several members of the medical faculty at the University of Heidelberg attempted to convince the Baden government to create a new position for an experimental physiologist. The most ardent of these advocates was Henle, who, since his appointment in 1843, taught anatomy, physiology, general pathology, and pathological anatomy. He had agreed to teach these courses at a time when physiological research had involved little more than microscopical anatomy accompanied by occasional chemical tests and investigations.69 But Helmholtz, du Bois-Reymond, Briicke, and Ludwig had begun to change physiology, and Henle, a man of the microscope, accepted and supported the growing divergence between their different methodological approaches to the study of organic processes. Between 1848 and 1852 Henle tried repeatedly to bring a young experimental physiologist to Heidelberg; Ludwig, Helmholtz, and du Bois-Reymond headed his list. Henle's efforts received strong backing from the state health commission. Consisting primarily of physicians, the commission controlled the state medical examination and granted medical licenses. Moreover, through its advisory capacity it influenced the kind of education and training offered to medical students. In the early 1850s, it began simultaneously to push for reform of educational and licensing

68. See, for example, "Wie sollen die Aerzte gebildet werden?'For a general discussion of the medical reform movement of the 1840s see the references in note 17. 69. Karl Rothschuh, "Von der Histomorphologie zur Histophysiologie unter besonderer Beriicksichtigung von Purkinjes Arbeiten," in J.E. PurkynP 1787-1869. Centenary Symposium, Prague, 8-10 Sepfember 1969, ed. Vladislav h t a (Bmo: Universita Jana Evangelisty PurkynE, 197 I), 197-2 12.

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43

requirements and to speak out strongly in support of the new experimental sciences. For example, in response to the government's request that it recommend whether the university should hire a zoologist or an experimental physiologist, the commission declared: To stay in the spirit of the times it is necessary to focus on cultivating the exact method in true scientific research and to train students more in the method of examining and utilizing natural objects. This being so, he [a zoologist] would not teach the subject of physiology in an up-todate fashion . . . , and another teacher, acquainted with the exact method and capable of heading a physiological institute with success, must be called in his place.'"

Although the commission did not succeed in convincing the government in 1852 to hire a physiologist, the issue did resurface four years later. The director of the health commission again centered his argument on the different methodological approaches of anatomists and physiologists. "Physiology," he wrote can be taught only by someone who is familiar with the exact sciences. The anatomist, even if he is very highly educated in his subject, is still engaged in a descriptive science, and this does not qualify him as a teacher of physiology. In physiology things must be explained; description is not enough. And if the [anatomy] teacher would nevertheless insist upon [teaching physiology] he would d o so in contradiction to the spirit of physiology, even hampering its d e ~ e l o p m e n t . ~ '

As these quotations attest, physicians too believed that changes in physiology, in particular the emergence of an exact method of investigation, held great consequence for medicine. This conviction reflected diverse assumptions and hopes. Those interested in the nature of disease, such as Henle and Virchow, believed that disease represented little more than the body's normal response to abnormal stimuli; thus, knowledge gained about the chemical and physical laws underlying physiological processes brought with it a greater understanding of the disease process. For those practicing medicine, by contrast, an increase in theoretical knowledge meant less than the gains they hoped for and envisioned in diagnostics and therapeutics. Practitioners could already 70. Die Sanitats-Commission to the Ministerium des Innern, 23 June 1852, Rep. 235131 33, Badisches Archiv. 7 1. Die Sanitats-Commission to the Ministerium des Innern, 10 December 1856, Rep. 235129872. Badisches Archiv.

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point to such diagnostic instruments as the ophthalmoscope, kymograph, and spirometer as evidence of the advantages experimental physiology could bring to medi~ine.'~ Although similar progress had yet to occur in therapeutics, physicians were convinced that experimental physiology had much to offer. Direct benefits perhaps belonged to the future, but experimental physiology still introduced students to "the spirit of the times" and "the spirit of physiology." By conducting physiological experiments the student learned a critical method that, medical reformers believed, would later help in the analysis of disease. The laboratory offered an opportunity to learn, under simplified and controlled conditions, an exact method of investigation; armed with these skills, the young student could enter the clinic prepared to confront the more complex phenomena of disease. In 1856, when Heidelberg began searching for an experimental physiologist who could teach physiology in "the proper way," it seriously considered all four members of the 1847 group. Yet there were clear favorites. Several members of the medical faculty, for example, expressed serious reservations concerning du Bois-Reymond, whom they criticized for his "excessive" specialization in nerve physiology. They were especially concerned that his teaching would be as specialized as his research-a serious criticism given their desire to attract medical students and to teach them the new methods of investigation. By contrast, the entire medical faculty favored Helmholtz, whom they thought the most capable of establishing a link between experimental physiology and medicine. Helmholtz, rather surprised at hearing this, wrote du Bois-Reymond that for some reason the Heidelberg medical faculty "does me the very questionable honor-I do not know why-of holding me to be less of a physicalist than the rest of our friend^."'^ Helmholtz's surprise is difficult to understand. Although his research had advanced the physicalist program as much as anyone else's, his invention of the ophthalmoscope and his work in physiological optics, as well as his five years of service as an army surgeon in Prussia, distinguished him from the other members ofthe 1847 group. No other member of the group would have been greeted as effusively as Helmholtz was when he finally accepted Heidelberg's offer. Shortly after he arrived in Heidelberg, a newly formed ophthalmological society honored him with a ceremony and a cup on which were inscribed (in 72. Although historians of medicine have argued convincingly that experimental physiology had little impact on therapeutics before the late nineteenth century, they have tended to overlook its impact on diagnostics. 73. Helmholtz to du Bois-Reymond. 5 March 1858, in Kirsten, 176-78. on 176.

Helmholtz and the German Medical Community

45

German) the words: "To the Creator of Modern Science, the Benefactor of Mankind, in grateful remembrance of the Discovery of the Ophthalm~scope."~~ That Helmholtz's appointment occurred squarely within a medical context is nowhere more evident than in the government's decision to institute new educational and licensing requirements in the very year that Helmholtz began teaching at Heidelberg. As already noted, local physicians' groups, backed by the state health commission, had been trying for almost a decade to convince the government to reform educational and licensing requirements so as to exert greater control over medical practice in Baden. The regulations in effect at mid-century had been issued in 1803 and had received only minor modifications since then. According to these regulations students had absolute freedom to study what they wanted (Lernfreiheit), meaning that a set curriculum could not be established. Moreover, to qualify for the state medical examination the student had only to fulfill the ambiguous requirement of having acquired "a thorough knowledge of the natural sciences and medicine."75 Shortly after Helmholtz's appointment, the Baden government replaced the lax curricular structure and the vague state examination procedure with specific detail and an exact system of requirements. In many ways the new curriculum moved in the direction of the one Helmholtz had followed at the Institut. Where Lernfreiheit had formerly ruled, students were now required to attend the university for at least four years before qualifying for the state examination. Moreover, the cumculum received more structure. During the first two years students had to attend general courses in the natural sciences, take two courses in dissection, and spend one semester each in the physiology and chemistry laboratories. In the latter two years they advanced to "medical courses" proper, including one year of practical work in the medical, surgical, and obstetrical clinics.7h The institutionalization of experimental physiology and the hiring of Helmholtz at the University of Heidelberg were thus important elements in the reform of medical education in Baden, and cannot be understood divorced from that context. Helmholtz's position was in 74. Quoted in Koenigsberger 1:314. 75. GroJherzoglich Badisches Sfaats- und Regierungsb[att, 5 August 1828 (Karlsruhe: Macklot, 1828). The laws and statutes dictating medical educational and licensing requirements until 1859 are collected in C.A. Diez, Zusammenstellung der gegenwartig geltenden Gesetze, Verordnungen, Instructionen und Entscheidungen uber das Medicinalwesen und die Stellung und die Verrichtungen der Medicinalbeamten und Sanitafsdiener im GroJherzogthum Baden (Karlsruhe: A. Bielefeld, 1859). 76. Mittheilungen des hadischen arztlichen Vereins 3 ( 10 February 1848):17-20.

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the medical faculty; his appointment coincided with a total restructuring of medical education; and one semester in the physiology laboratory became a requirement for medical students. In the "spirit" of scientific medicine, students were introduced during laboratory instruction to common microscopical and chemical techniques, such as the preparation of bone sections and injections, and the analysis of urine and creatine. Moreover, they conducted physiological experiments proper, inducing the contraction of frog legs, cutting superficial nerves, and simulating digestion, for example. Two to three hours of instruction were offered each week, and the laboratory, under the watchful eye of a supervisor, was open every morning from eight to twelve o'clock in order to provide students with the opportunity to perfect their techniques or to do their own experiment^.^^ The supervisor was not, however, Helmholtz, but one of his assistants (e.g., Wilhelm Wundt). Indeed, Helmholtz soon expressed skepticism about the wisdom of this laboratory requirement. Shortly after his arrival in Heidelberg he characterized (to du Bois-Reymond) the "legal regulation which turns the physiology course into a required course for Baden students" as an "exaggeration of enlightened principles." He feared especially that "it could become very burdensome" for him.78He soon solved this problem, however: he made sure he had little to do with this laboratory instruction. Unlike Ludwig, who involved himself directly in his students' work, and whose interest and excellence in teaching techniques and methods attracted individuals from all over the world, Helmholtz remained aloof from the routine drills conducted in his laboratory. These became the sole responsibility of his assistants. Moreover, he further distanced himself from his "medical" duties by requiring his assistant to teach his courses in microscopical anatomy, justifying this by his lack of histological knowledge and his tendency to get headaches from looking . ~ the ~ years Helmholtz spent at Heidelberg, through a m i c r o ~ c o p eIn he lectured only on subjects he enjoyed, alternating between a general human physiology course one semester and a more specialized course on the physiology of the sense organs the following semester.80 Much 77. Wolfgang G . Bringmann, Gottfried Bringmann, David Cottrell, "Helmholtz und Wundt an der Heidelberger Universitat 1858- 187 1," Heidelberger Jahrbiicher 20 (1976):79-88, on 81-5; and Wilhelm Wundt, Erlebfes und Erkanntes (Stuttgart: A. Kroner, 1921), 154. 78. Helmholtz to du Bois-Reymond, 29 October 1858, in Kirsten, 193-94, on 193. 79. Bringmann, et al., "Helmholtz und Wundt," 79-88. 80. Anzeige der Vorlesungen auf der GroJ3herzoglich Badi.schen Ruprecht Karolinischen L'niversitat zu Heldelberg (Heidelberg: n.p., 1858-71).

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47

had changed since his days in Konigsberg, where he had been responsible for anatomy, pathological anatomy, and pathology, in addition to physiology. By the 1850s and 1860s, experimental physiology had gained disciplinary autonomy, permitting Helmholtz (and others) to focus their time and energy on their specialized areas of interest. A paradoxical situation thus arose: the institutionalization of experimental physiology had occurred because of its perceived medical significance, yet this same institutional support granted Helmholtz more license than ever to pursue his own interests, be they medical or otherwise. Baden had hired him and built him a brand new laboratory as part of its reform of the medical curriculum, yet for the first time in his career Helmholtz did not have to teach routine medical courses. Helmholtz did not, however, cut all ties with medical students. On the contrary, he welcomed advanced students into his laboratory who were interested in clinical work in ophthalmology and ophthalmometry. Emanuel Mandelstamm, M. Woinow, and Knapp, for example, all came to Heidelberg after studying with von Graefe in Berlin in order to learn the theoretical underpinnings of their specialty. Knapp even stayed on to write his Habilitation on the curvature of the human cornea and to teach ophthalmology at the university.*' Nevertheless, in the thirteen years Helmholtz spent at Heidelberg, his work gradually took him out of a medical context. Despite his pursuit of physiological optics and acoustics until 1863, his research increasingly turned to questions of epistemology, aesthetics, and ultimately to mathematics and physics. In 1871 he finally left Heidelberg to accept a position as professor of experimental physics in the philosophical faculty at the University of Berlin.

5. Epilogue During the last twenty-three years of his life, Hlelmholtz focused his teaching and research on physics, the subject that had intrigued him since his childhood. Much of his time in Berlin was spent, moreover, in planning and then presiding over the Physikalisch-Technische Reischsanstalt, which opened its doors in 1887.82These new activities may have weakened Helmholtz's links to the medical community, but 81. Biographisches Le-xikon, S.V. "Mandelstamm, Emanuel"; "Woinow, M."; and "Knapp, Hermann Jakob." 82. David Cahan, An Instltute.for an Empire: The Physikalisch-Tcchnische Reichsanstalt 1873-1918 (Cambridge: Cambridge University Press, 1989). chaps. 1-3.

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his old ties were never entirely broken. He continued to receive honors for the work he had done in ophthalmology until well into the 1 8 8 0 ~ ; ~ ~ and in 1877 he accepted the professorship in physics at the Institut. Asked to give the keynote address that year to the incoming class, he spoke about his own medical education, recent changes in ~~iedicine, and the direction he believed (and hoped) future medical education and research would take. Although the occasion and setting doubtless encouraged some rhetoric on Helmholtz's part, he nonetheless sincerely claimed that at a time when education had been based largely on book learning, his medical studies had "taught me more forcibly and more convincingly than any other training could have done the eternal principles of all scientific These principles included independent observations, the construction of theories based on such observations, and the testing of these theories in practice. Physicians, he concluded, must for this reason always play a prominent role in the work of true enlightenment, for among those who must continually a n d actively verify their knowledge by testing it against nature, physicians begin with the best mental p r e p a r a t i ~ n . ~ ~

Helmholtz himself chose a career that did not require him constantly to test his theories "in practice," yet this may be one reason he appreciated the importance throughout his years as a physiologist of maintaining a link with the medical community. Medicine, Helmholtz once wrote, was little more than the practical side of p h y ~ i o l o g y . ~ ~ Here he echoed the views of medical reformers who believed medicine would become a science when practitioners began applying at the bedside both the knowledge and the methods they had learned in physiological laboratories. For these reformers, Helmholtz had been one of the outstanding symbols of the new scientific medicine. As we have seen, this image-and it was one Helmholtz had helped popularizehad assisted Helmholtz in achieving his career goals, being largely responsible for his appointment to the chair of physiology at the University of Heidelberg. Yet the advantages he accrued from his connection to the medical community extended well beyond these professional gains. Through the application of his theories and instruments in a clinical setting, Helmholtz also received evidence not only of the 83. In 1885, e.g., he received the Graefe-Medaille from the Ophthalmologische Gesellschaft. See "Antwortrede gehalten beim Empfang der Graefe-Medaille zu Heidelberg 1886," V'Rj 2:311-20; and Koenigsberger 2:337-41. 84. "Das Denken in der Medicin," VR32: 169. 85. Ibid.. 190. 86. "Ueber das Ziel und die Fortschritte der Naturwissenschaften." VR3 1:361.

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validity but also of the usefulness of the knowledge he produced. That this pleased him is nowhere more evident than in the popular speech he gave in Heidelberg in 1862 on the occasion of his election to the office of university rector. As he told his audience: Knowledge itself is not the object of people on earth. . . . Only action gives a person a dignified life; therefore his goal must be either the practical application of his knowledge o r the increase in knowledge itself.s7

Helmholtz may have dedicated his life to the latter, but his contributions to the former were significant as well. Indeed, without them it is impossible to understand his early career.

87. "Ueber das Verhaltniss der Natunvissenschaften zur Gesammtheit der Wissenschaft." in l.R1 1:l 17-45. quote on 140.

Experiment, Quantification, and Discovery Helmholtz's Early Physiological Researches, 1843-50

Kathryn M. Olesko Frederic L. Holrnes

1. Introduction

Before Hermann Helmholtz took up the work for which he became best known in sensory physiology, he published four investigations in general physiology between 1843 and 1850. The first, on putrefaction and fermentation, was well conceived but inconclusive. The next three-those on muscle and nerve physiology (1845, 1848, and 1850)became classics. Each defined a problem of fundamental importance. Through an elegant experimental design often requiring precise quantitative results, each resolved issues posed simply yet decisively. Moreover, each germinated a thriving subfield of investigation within the burgeoning field of mid-nineteenth-century experimental physiology. Historians have examined Helmholtz's experiments of 1843, 1845, and 1848, addressing them primarily within the context of broader theoretical issues, especially theories of animal heat, Helmholtz's formulation of the principle of conservation of force, and his opposition to conceptions of vital force.! Although he pondered these and other conceptual issues as he worked on these experiments, his investigative pathway was also shaped by an increasingly penetrating understanding of the limitations posed by his research methodology's techniques. 1. The most recent studies are Timothy Lenoir, The Strategy of Life: Teleology and Mechanrcs in Nineteenth-Century German Brology (Dordrecht: D. Reidel, 1982), 1972 15, 231-35; and Richard Kremer, The Thertnodynamics of Life and Experimental Phvsiology. 1770-1880, Harvard Dissertations in the History of Science, ed. Owen Gingerich (New York and London: Garland Press, 1990), 237-55, 275-307.

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Even though in each of these cases he either pushed existing methods to their limits or surpassed current practice so as to redefine a problem at a higher level, he was also acutely aware that his results sometimes only established the boundaries within which exact solutions resided. This awareness was especially prominent in his adaptation to physiology of precision-measuring techniques, an area in which he quickly became a leading craftsman and innovator. Historians have also examined Helmholtz's deployment of precision techniques, especially his modification of instruments; yet several issues remain ~ n e x a m i n e dThese .~ include his use of various forms of quantification associated with precision measurement and their interaction over time, and how his methods evolved from his earliest investigations up through his painstaking and delicate measurements of the propagation velocity of the nerve impulse in 1849 and 1850. The historically significant role of precision measurement in mid-nineteenth-century German science itselfjustifies a detailed study of Helmholtz's early investigative techniques; for Helmholtz, like many other investigators, recognized the power of precision. An examination of his techniques is also important for gaining a perspective on the crucial transformation in German science during the second half of the century to non-precision forms of experimentation; for Helmholtz, in the course of his nerve investigations, did not always achieve the precision he believed he needed, nor did he necessarily believe that quantitative exactitude was always essential or even appropriate for convincing others of his findings. His ability to extract from simpler techniques what he considered to be adequately certain results helped to diminish reliance on certain forms of precision measurement in the construction of scientific knowledge. As one of his rare and hitherto unstudied laboratory notebooks reveals, his passage to simpler forms of error and data analysis ironically began during the course of an investigation whose results were made possible only by the most complex techniques of contemporary precision measurement, that of measuring the velocity of the nerve i m p u l ~ e . ~

2. Here, too, the most recent studies are by Timothy Lenoir, "Models and Instruments in the Development of Electrophysiology," HSPS 17 (1986):l-54; and Kremer, Thermodvnamlcs of Lfe, esp. 275-307. Kremer's solid study, with its comprehensive view of Helmholtz's early physiological studies, especially of his use of instruments. greatly aided us in the preparation of the present essay. One way in which this essay differs from Kremer's is in its analysis of Helmholtz's treatment of data. 3. AW, No. 547: Untersuchungen uber Muskeln und Nemen. We treat this laboratory notebook in detail in our book on Helmholtz's early scientific career (in preparation). There may be other extant laboratory notebooks written either by Helmholtz or his students: see, e.g.. AW, No. 544: Versuche uber Muskelton (Mai 1866-Februar 1867).

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This essay examines Helmholtz's early physiological experiments and focuses especially on the techniques that dominated his early investigations: the instrumental and quantitative techniques of exact experiment. Precision measurement became an issue for Helmholtz as early as his third scientific publication, that on muscle physiology, when the physiological questions that he posed began to exceed the technical means at his disposal. As Section 2 of this essay shows, through his investigations from 1843 to 1845 Helmholtz came to see that he could conduct deeper, more rigorous, and more quantitative physiological investigations than others before him, thereby helping to transform the nature of experiment in physiology. Moreover, by criticizing previous studies in physiological heat, Helmholtz sharpened his own understanding of the conditions under which data is produced and the nature and quality of data, as Section 3 demonstrates through its analysis of Helmholtz's 1845 review article on these studies. Section 4 of this essay then turns to an analysis of Helmholtz's route to his 1848 paper on the formation of heat in muscles. It shows how Helmholtz adopted and adapted a series of instruments and apparatus-including a multiplicator, thermoelectric circuits, and an induction coil-and how he learned to adjust his experimental set-up to meet a series of experimental goals, including the source of animal heat. Having just promulgated in 1847 his principle of force conservation and working within a broad physicalist program, Helmholtz further adapted, as Section 5 shows, instruments and measuring techniques, specifically Eduard Weber's muscle-contraction apparatus and Carl Ludwig's apparatus for graphically recording physiological effects, that in 1850 allowed him to measure muscle-contraction times. Section 6 concerns Helmholtz's preliminary results of 1849-50 on measuring the propagation velocity of the nerve impulse. It especially draws attention to the ways in which Helmholtz tried to convince others of the certainty and demonstrability of his findings. Section 7 then analyzes his use of quantitative error analysis (in particular, the method of least squares) in his discovery of the propagation of the nerve impulse. Finally, Section 8 briefly reflects on the larger meaning of that discovery, both for Helmholtz's own emergence as a master of instrument analysis and design and for the stimulation it brought to several scientific fields.

2. Helmholtz's First Quantitative Muscle Experiments Before precision measurement became an issue for Helmholtz in his work on muscle physiology, he had already mastered the principles

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of anatomical observation and the techniques of chemical experimentation in the Berlin laboratories of Johannes Muller, Eilhard Mitscherlich, and Gustav Magnus. Under Miiller's guidance in particular, Helmholtz had displayed considerable technical skill in the delicate dissection of small invertebrate tissues and in microscopic observat i ~ n Although .~ historians have recently made much of the philosophical differences between Miiller and his student^,^ there is no evidence that any of them quarrelled with Muller or that he lessened his high regard for them. Miiller and his students shared a common commitment to rigorous standards of investigation, employing the most effective methods available from anatomy, experimental physiology, physics, and chemistry. Miiller's example reportedly inspired Helmholtz to decide, even before he completed his medical degree (November 1842), to pursue methodologically rigorous investigations whose results he could bring to bear on the broad questions about vital processes that stirred him.6 After graduation, Helmholtz took up the problem of "the basis of the so-called spontaneous decomposition processes [fermentation and putrefaction] of organic substances deprived of life," a question over which he thought that "among chemists and physiologists highly contradictory views have prevailed."' The new problem also required him to acquire additional scientific skills. To the microscope he now added chemical methods of investigation, probably learned under Mitscherlich. Helmholtz's definition of the problem of investigating fermentation and putrefaction was neither original in its definition nor its methods.* His aim was not to discover novelty but rather to exert an experimental critique capable of resolving a disputed issue. By adopting and refining

4. See, for example, Helmholtz's 1842 doctoral dissertation under Muller, De Fabrica Systematis Nervosi Evertebratorum, Inaugural-Dissertation (Berlin: Typis Nietackianis, 1842), in WA 2663-79. 5. Muller's students have recently been described as in "rebellion" against him; see Lenoir, Strategy of Life, 195; cf. Kremer, Thermodynamics of Life, 30511. 6. Koenigsberger 1:5 1-2. 7. "Ueber das Wesen der Faulniss und Gahrung," MA (1843):453-62, on 453, in WA 2:726-34. 8. Cf. the work of his predecessors, including: Theodor Schwann, "Vorlaufige Mittheilung, betreffend Versuch uber die Weingahrung und Faulniss," AP 11 (1837): 18493; Joseph Gay-Lussac, "Extrait d'un mimoire sur la fermentation," Annales de Chimie 76 ( 1 81 0):245-59; Justus Liebig, "Ueber die Erscheinungen der Gahrung, Faulniss und Venvesung und ihre Ursachen," Annalen der Pharmacie 30 (1 839):250-87, 363-68. For a comprehensive treatment of the history of fermentation, see Joseph Fruton, Molecules and Life: Historical Essays on the Interplay of Chemistry and Biology (New York: WileyInterscience, 1972), 22-86. Helmholtz's later experiments on the matter are outlined in AW, No. 666: Versuch uber Gahrung bei Magnus, which describes experiments performed in Gustav Magnus's Berlin laboratory during the winter of 1845-46.

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Physiologist

methods that others had already devised, he attained results similar to theirs but which closed loopholes and reduced uncertainties. In principle, Helmholtz's experiments appear to have provided sufficient evidence to show conclusively the dependence of both fermentation and putrefaction upon microorganisms. In fact, the issue remained disputed, and Justus Liebig's chemical decomposition theory retained an influence for nearly two more decades until overtaken by Louis Pasteur's dramatic refutation^.^ Although the historical effect of Helmholtz's published work on fermentation and putrefaction was limited, it was, for the evolution of his own investigative powers, a major step. Undertaking for the first time to solve a central contemporary problem through experimental means rather than observation alone, Helmholtz improved methods that his able predecessors had introduced. He showed signs of a capacity to master experimental techniques from another field; to adapt and combine them to center in on the key points ofa disputed question; to maintain controls; and to arrive at results more definitive than those of his predecessors. Nonetheless, his reported results did not sufficiently emphasize the power of his methods. Still, the investigation of putrefaction and fermentation provided an entree into more controlled observation, in the form of experiment, than he had previously practiced. Not until late 1843 did Helmholtz begin to develop more exacting and quantitative procedures of investigation. While working as an army physician in Potsdam, he embarked upon experiments aimed at establishing whether or not the chemical composition of a muscle changes when it is stimulated to prolonged activity.1° At the opening of his 1845 paper on the subject, he presented his reasons for having taken up this investigation in 1843: One of the highest questions in physiology, touching directly upon the nature of the vital force-namely, whether the life of the organism is the effect of its own self-regenerating,purposefully acting force, or the result of forces that are active also in lifeless nature, only specially modified by the nature of their combined actions-has in recent times taken on, with special clarity in Liebig's attempt to derive physiological facts from known chemical and physical laws, a much more concrete form; that is, whether or not the mechanical force and the heat created in the organism can be derived completely from the Stofwechsel." 9. Fruton, Molecules and Llfe, 49-63. 10. Koenigsberger 154-5. 1 I. "Ueber den Stoffverbrauch bei der Muskelaction," MA (1845):72-83, on 72, in U:4 2735-44. On the long-range implications of this investigation see Frederic L.

Experiment, Quantification, and Discovery

55

Helmholtz hoped to answer experimentally not the entire question that he had posed, but rather the more limited one of whether it could be shown that "in the production of mechanical effects . . . matter is consumed." Although physiologists had long assumed such a consumption from the common experience of fatigue after exertion and gradual recovery, "scarcely any ideas had been established about the nature of the matter consumed and the location of the transformations." Moreover, Helmholtz noted that "there is still lacking a knowledge of all of the beginning and intermediate links of the process and the place in which they are formed, and since inference based on the end products found in the excretions must always remain problematic, I decided to try an entirely direct way to investigate them."12 He adopted a strategy of stimulating electrically one pair of isolated frog muscles to contract repeatedly until it was exhausted, and then comparing its chemical composition with that of the non-stimulated muscle. Since galvanic currents themselves produced chemical changes that might be mistaken for those he sought to detect, Helmholtz reverted to the eighteenth-century method of charging a Leyden jar from an electrostatic generator and stimulating the frog muscle by means of its rapid intermittent discharges.13 Far more difficult technically was the problem of identifying the chemical changes that might have occurred through the activity of the stimulated muscle. Jons Berzelius, who pioneered quantitative work on this problem, was acutely aware of the inadequacies of such analyses. In January 1830, as he completed the work necessary to write the section on animal chemistry for his textbook, he wrote to Mitscherlich: I have been occupied this winter with little else than the chemistry of animals, which is not the most pleasant [of subjects], because in this area, no matter how much interest one may take in it, the uncertainty of the results and the impossibility of controlling them sufficiently is always unsatisfying; but to know something with certainty is the greatest satisfaction that an investigation can bring to one.14

The situation had changed little when Helmholtz began his own investigation thirteen years later. Relying on methods similar to those Holmes, Between Biology and Medicine: The Formation of Intermediary Metabolism (Berkeley, Calif.: Office for History of Science and Technology, 1992). 12. "Stoffverbrauch," 73. 13. Ibid., 74. 14. J.J. Berzelius to E. Mitscherlich, 19 January 1830, Mitscherlich NachlaB 165, Deutsches Museum, Sondersammlungen, Munich.

56

Physiologist

that Berzelius had used to extract and identify substances from animal matter, Helmholtz found that the discriminating quantitative results he needed were not easy to achieve. Even if he was already familiar with the methods of animal chemistry he must have spent a considerable part of the two years he devoted to his investigation of muscle contraction gaining sufficient proficiency with these methods to deploy them on a problem that made unprecedented demands on them for quantitative discrimination. Helmholtz considered it "a priori" probable that "the muscle fiber [identifiable with Berzelius's "solid part" of the muscle] takes part in the decomposition," "because we generally find protein compounds as carriers of the highest vital energies," and because the increased quantities of phosphates and sulfates in the urine found after muscular exertion might well have derived from the decomposition of the protein.15Although Helmholtz placed his discussion of muscle fiber near the end of his published paper, his initial expectation suggests that he may well have tried early on in the investigation to find out if it is decomposed. "A direct decision through experimentation has not been possible until now," he reported, because the error, which arises from the uncontrollable greater or lesser filling [of the muscle] with blood and the greater or lesser absorption of moisture, makes the relative proportion of the solid part not accurately enough comparable. The observed weighings varied, so that sometimes one side, sometimes the other side was around one-fourth to one-half percent greater, and the possible decomposition of the muscle fiber might not exceed this amount.'"

That he sought to detect a change expected to be a fraction of one percent of the quantity of muscle fiber present is itself a revealing indication of the extent to which Helmholtz was pressing the limits of the available analytical means; for normally, errors in similar experiments could be ten to one hundred times higher. "Among the soluble constituents," Helmholtz wrote, "the albumin was investigated first." He found, however, that the uncontrollable variations, including the range in the amount of albumin, so exceeded the average percentage difference as to prohibit drawing decisive conclusions from his results. His dismissal of these results, which had been difficult to achieve, seems to have been based merely on an intuitive sense that they were indecisive. Yet from previous analyses of 15. "Stoffverbrauch." 82. 16. Ibid.

Experiment, Quantification, and Discovery

57

Berzelius and others, Helmholtz knew that there remained in the solution from which the albumin had been separated the substances known collectively as the "extractive matter" of the muscle. Following approximately Berzelius's procedures, he separated them into "aequous," "spiritous," and "alcoholic" extracts. When he dried and weighed these various extracts, he again encountered irregularities that interfered with an accurate determination of their absolute weights; but in this case the difficulty did not prevent him from reaching significant comparative results. He wrote: If one takes care that all of these operations are carried out in exactly the same manner and under exactly the same conditions with both portions of muscle, one obtains correct figures for the relative proportions, even with a less-careful determination of the absolute quantities. To determine the latter involves great difficulties, because one does not always succeed in washing the filtrate completely out of the organic matter, which is not easily filterable. I have, however, convinced myself through special experiments that the quantities remaining behind are too small to have an influence on the result. For these extracts the result turns out to be, in all experiments without exception, that the aequous extract is diminished in the electrified portion of muscle and, inversely, the spiritous and alcohol extract are increased in comparison to the non-electrified portion.I7 Helmholtz summarized the results of nine "more accurate trials" (Figure 2.1). "The result stated above emerges clearly in these figures," he asserted, even though the ratios a:h and c:d in the second table still vary greatly, which may derive partly from the greater or lesser intensity of the contractions that may be induced in the unelectrified muscle through its preparation, air, or warm water. It should be noticed that the average difference in the aequous extracts of 0.3 corresponds rather well to the spiritous extract of 0.24.18 In his determination and analysis of the extracts Helmholtz thus realized that obtaining meaningful results depended on what was then known as the method of repetition: maintaining "exactly the same conditions" in one trial after another. Although his quantitative assessment of experimental errors was not as sharp as those routinely performed in physics, it seems to have been primarily the nature of 17. Ibid., 76-7. 18. Ibid.. 78.

58

Physiologist

- Alkol

nkt

m

c

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,

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b) im laicht cleklrisirten :leiache.

1

hll,nisa

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I

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.l

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/

,

-

v l r ~ rl t u a l : ~ l r ~t k

La\ mlc2> C', then (a~-,,/at)~ is positive and greater than 2c2,hence ar,,/at is a real number. If this term ar12/atis positive, r12will increase until Q,Q2/r12= m,c2, hence ar,,/at increases to in-

28. "Ueber die Theorie der Elektrodynamik," 640-43; "Ueber die Theorie der Elektrodynamik. Kritisches," 659-61; Whittaker, History 1:203; and Kaiser, Theorien der Elektrodynamik, 101-4. 29. "Ueber die Bewegungsgleichungen der Elektricitat," 578-81. 30. Ibid., 550-51, 583; and A.E. Woodruff, "The Contributions of Hermann von Helmholtz to Electrodynamics," Isis 59 (1968):300-11, on 304-5. 31. "Ueber die Bewegungsgleichungen der Elektricitat," 553-54.

Formation of Classical Electrodynamics

385

finity. The same will occur when, in the beginning, C' > m,c2 > Q1Q2/ r,, and ar,,/at is negati~e."'~For finite values of m,c2 and Q1Q2/r12 the square of the relative velocities in Weber's potential can obviously become infinite. In arguing against Weber, Helmholtz introduced the simplest case of two "isolated," moving electrical particles interacting electrodynamically according to Weber's law. Although these moving particles do start with finite kinetic energy, when approaching one another or moving apart they could gain infinite kinetic energy in a certain small but finite distance. Thus a system of interacting moving charges like that described by Weber's law seemed to become unstable, for the time integral, or the equation for the conservation of energy, loses all meaning. Although in the course of his debates with Weber and with Carl Neumann, a mathematical physicist at the University of Leipzig and the son of Franz Neumann, Helmholtz later varied his argument slightly, he stuck to this salient point t h r o ~ g h o u t . ~ ~ Circa 1870 neither Weber nor Carl Neumann nor anyone else could present experimentally confirmed knowledge of the velocity of light as an upper limit or could give numerical values for molecular forces. The values for molecular radii, calculated approximately by Kirchhoff in 1866, were highly loaded with uncertain, basic assumptions about the kinetic theory of gases (for example, the concept of a mean free path) and thus open to criticism. Accordingly, Weber thought that applying his law to freely moving charges-that is, to elementary particles, not to constituent parts of an electric current-might only provide a hint of the problems of particles interacting within extremely small microphysical distances. Although Weber clearly thought in terms o f a molecular structure for matter, he realized that the molecular forces which came into play within those microphysical dimensions necessarily limited any macroscopic electrodynamic force law to a sort of preliminary survey of the field of microphysics. He thus argued in 1871 that Helmholtz's objections, which in the first instance applied to extremely small molecular distances and so were still not within the reach of experimental physics, might not be generally valid.34However, in 1873 Helmholtz countered by showing that this operational argument might be incorrect or could at least be avoided by introducing 32. Ibid., 553. 33. "Ueber die Theorie der Elektrodynamik," 639-45; "Ueber die Theorie der Elektrodynamik. Kritisches"; "Kritisches zur Elektrodynamik," A P 153 (1874):545-56, in W,4 1:763-73. 34. Wilhelm Weber, "Elektrodynarnische Maassbestimmungen[,] insbesondere iibcr das Princip der Erhaltung der Energie," [I 8711, in Werkc (Berlin: J . Springer, 1894), 4:247-99, esp. 247-49. 268-69, 298.

386

Physicist

additional, nonelectric forces. He argued that if, for example, a charged particle moves (even) in a frictional medium, then it might accelerate continuously under the influence of a charged sphere, which could initially be a great distance away.35In turn, Carl Neumann, like Weber before him, rejected this argument, questioning its operational meaning. Neumann explicitly denied that Helmholtz had shown the operational meaning for the special microphysical case, wherein Weber's law led to a violation of the principle of conservation of energy. Until Helmholtz could demonstrate how this special case could in fact occur, and until a physical measurement could be obtained, Neumann chose to reject Helmholtz's argument as a test case of Weber's law.36 Neither the philosophical nor the physical arguments of the WeberHelmholtz debate led to a decisive result-perhaps because Weber, Neumann, and Helmholtz were unable to disentangle their dispute from the confusion about the appropriate physical levels (microphysical and macrophysical) to be considered. They could not agree on the limitations of a macroscopic law with regard to the problems arising from microphysical distances. Equally important, Helmholtz's test cases, which actually included the interplay of open currents in general, had not yet been subjected to experimental ~erification.~' Moreover, the personal relations between Weber and Helmholtz became troubled in the early 1870s after Helmholtz became the object of a vitriolic polemic instigated by the astrophysicist Friedrich Zollner, one of Neumann's colleagues at Leip~ig.'~ Zijllner, who became a close friend of Weber's during the 1870s, wanted to compromise Helmholtz in his relations with Weber's British critics, namely, Peter Guthrie Tait and William Thomson. Helmholtz's preference for Maxwell's theory and his dislike of Weber's was continuously nourished by his unceasing doubts about the wisdom of an electrodynamic force law which, unlike a mechanical force law, depended not only on distances but also on velocities and

35. "Ueber die Theorie der Elektrodynamik," WA 1:647-87, esp. 663-68; and Woodruff, "Contributions." 305. 36. Carl Neumann, "Ueber die gegen das Weber'sche Gesetz erhobenen Einwande," .4P 155 (1875):211-30, on 226. 37. "Versuche iiber die im ungeschlossenen Kreise durch Bewegung inducirten elektrornotorischen Krafte," AP 158 (1875):87-105, in U7A 1:774-90. 38. Koenigsberger 1: 148; Woodruff,"Contributions," 305; Friedrich Zollner, Ueber die Natur der Cometen. Reitrage zur Geschichte und Theorie der Erkenntniss (Leipzig: Engelmann, 1872), v-lxxii, xcvii-c; Helmholtz's preface to William Thomson and Peter Guthrie Tait, Handbuch der theoretischen Phvsik, trans. H . Helmholtz and G. Wertheim, 1 vol. in 2 parts. (Braunschweig: Vieweg, 1871-74), 2:v-xiv; and J. Hamel, "Karl Friedrich Zollners Tatigkeit als Hochschullehrer an der Universitat Leipzig," NTM 20 (1983):35-43.

Formation of Classical E l e c t r o d y n a m i c s

387

on accelerations as ~ariables.3~ Moreover, Helmholtz was also probably reluctant to accept Weber's complicated dual-conduction mechanism, which was an essential part of Weber's derivation of the law of electromagnetic induction and which, in effect, reconciled his electrodynamic law with the Galilean invariance as given in the equations of classical mechanics.40 Nonetheless, Helmholtz did more than simply criticize Weber's electrodynamic law and praise Maxwell's theory. For he sought to orientate himself and others in the "pathless wilderness" of competing theories in electrodynamics around 1870;41it was in this historical context that he promulgated his own contribution to the ongoing discussion about a fundamental potential for current elements. As already noted, those current potentials were mathematical tools used to derive further equations. Thus, the negative gradient of the potentials (the variation with respect to changing position) furnished laws of ponderomotive forces, that is, laws of mechanical forces between distant linear currents. The time derivative of the potentials furnished the electromotive force induced in systems of time-variant currents. With regard to a fully developed field theory of electrodynamics, those (vector) potentials for currents and (scalar) electrostatic potentials could provide a means to uncouple the field equations in order to derive, for example, separate wave equations for the propagation of electric and magnetic fields. Helmholtz thus established the following equation for a general vector potential U,:

where i,ds', and i,dS, are the respective current elements, c a constant of the order of magnitude of the velocity of light, i,, the distance vector of the current elements, and k a variable factor which could assume the values - 1, 0, and Helmholtz tried to adjust his own generalized potential to Neumann's potential (where k = 1) and, notwithstanding his own objections, to Weber's potential (where k = - I). For k = 0, Helmholtz's potential also supposedly embraced a formula

+

39. "Kntisches zur Elektrodynamik," 772; and "Ueber die Theorie der Elektrodynamik. Zweite Abhandlungen. Kritisches," 684-87. 40. Hans-Jiirgen Treder, "Helmholtzsche und relativistische Elektrodynamik," Beilruge zur Geophysik 79 (1 970):401-20, on 4 14-1 6; and idem. "Helmholtz' Elektrodynamik und die Beziehungen von Kinematik, Dynamik und Feldtheorie," WZHL'B 22:3 (1973):327-30, on 328. 41. R. Steven Turner. "Hermann von Helmholtz." DSB 6:241-53, on 250. 42. "Ueber die Bewegungsgleichungen," 567.

388

Physicist

Maxwell implicitly ("in verdeckter Form") used to derive his law for ' what Helmholtz claimed and electromagnetic i n d ~ c t i o n . ~However, what often is cited without proof, is far from being obvious in Maxwell's own The only expression comparable to Helmholtz's general electrodynamic potential was that which appeared in Maxwell's derivation of the coefficients of mutual electrodynamic induction. These induction coefficients were a formal tool for introducing the precise geometrical location of interacting currents and for eventually calculating the energy of a system of interacting currents. But Maxwell did not use any explicit formula which can be considered a special form of Helmholtz's expression for a general potential. Maxwell's potential is only comparable to Helmholtz's potential when it is integrated for closed circuits; in this case both expressions are identical. Helmholtz's expression for a generalized potential also agreed with the formal structure of Maxwell's theory insofar as Helmholtz assumed that

where 4 is the electrostatic "potential function of the free elect~icity."~~ When k = 0 this equation is equivalent to a formal condition which (to use modern terminology) is known as the Coulomb gauge, a condition which in fact Maxwell assumed in his presentation of the general equations of the electromagnetic field.46 To obtain an idea of the status of Helmholtz's general potential within a more complete theory of electrodynamics, consideration is needed of how his potential functioned in his system of differential equations for the "movement of electricity," equations which did not yet include the influence of dielectric and magnetic properties of matter. When discrete current elements were replaced by continuously distributed current densities, then Helmholtz's potential became primarily a solution to his main differential equation,

43. Ibid., 548-49. 44. See, e.g., James Clerk Maxwell, "A Dynamical Theory of the Electromagnetic Field," [1864/1865], reprinted in Niven, ed., Scientific Papers 1:526-97, on 589-90. 45. "Ueber die Bewegungsgleichungen." 572. 46. Ibid.; Woodruff, "Contributions," 303-4; and Treder, "Helmholtzsche Elektrodynamik," 419.

Formation of Classical Electrodynamics

389

which summarized the electrodynamic effects of a given current density j (or one originating from electromagnetic induction) and the electrostatic effects of free electric charges. Yet only by assuming k

=

0 or div U"

a 2 u

=

0, and only by neglecting -,

at2

is Helmholtz's

equation compatible with modern theory.47 In fact, Helmholtz's general potential, as Jed Z. Buchwald has argued, had a far more limited predictive capability than Maxwell's field theory and Weber's electrodynamics of moving charged particles. Helmholtz's own understanding of his potential as embracing all possible electrodynamic interactions did, however, open a way for new experiments striving for unknown interaction states of objects carrying time-variant charges and

4. Helmholtz's Theory of the Electromagnetic Field Helmholtz's criticism of Weber's theory as well as his own proposal of a fundamental electrodynamic law were motivated and nurtured by his attempt to reconcile electrodynamics with the principle of energy conservation. At the same time his efforts were also inseparably linked with his struggle to understand Maxwell's new theory of an electromagnetic field. As early as 1870, while speaking of the power of Maxwell's theory, Helmholtz presented his own contribution to electromagnetic field theory, one which competed with Maxwell's. At the time, the competition was not one of professionals of equal status. Maxwell's standing within the scientific community before 1871, when he became the new Cavendish professor of natural philosophy at Cambridge, was distinctly less than that of Helmholtz. Indeed, in a biographical portrait of Helmholtz in 1876 Maxwell himself referred to the overwhelming, universal scientific work of Helmholtz and called him an "intellectual giant."49 Nonetheless, as was the case with Helmholtz's fundamental law for the interaction of current elements within the context of general elect r o d y n a m i c ~his , ~ ~field theory soon fell behind Maxwell's theory, even 47. "Ueber die Bewegungsgleichungen," 568-77; John David Jackson, Classical Electrodynamics (New York, London, Sidney: John Wiley, 1962), 182; and Harald Stumpf and Wolfgang Schuler, Elektrodynamik (Braunschweig: Friedrich Vieweg und Sohn, 1973). 54. 48. See Jed Z. Buchwald's essay, "Electrodynamics in Context: Object States, Laboratory Practice, and Anti-Romanticism," in this volume. 49. James Clerk Maxwell, "Hermann Helmholtz," [1877], in Niven, ed.. Scient~fic Papers, 2:592-98, on 598. 50. See, e.g., his Vorlesungrn uber Theoret~schePhysik, vol. 4: Vorles~ingeniihrr Elektrodynamik und Theorie des Magnrtismus. 34 1 .

390

Physicist

as his approach had an enormous impact on the process of reception of Maxwell's theory by Continental physicists. As with the impact of Helmholtz's fundamental law, it was his approach to electrodynamic field equations-that is, its formal generality-that attracted the attention of Continental physicist^.^' Indeed, Buchwald has even gone so far as to argue that, except for Foppl's textbook of 1894, all Continental attempts to understand Maxwell's theory did so only "as a limiting case of Helmholtz's" theory.52 Generality came into Helmholtz's theory, in the first place, through an adaptive factor k in his generalized vector potential uH.This generalized potential uHcontributed not only to the various discussions of the fundamental laws for the elementary electrodynamic interaction but also to the inner foundation of Helmholtz's own differential equations for "moving electricity" and eventually to his development of a complete alternative to Maxwell's field theory, including the influence of matter on electrodynamic action.53Thus this generalized potential appeared again in a number of places in Helmholtz's elaborate electrodynamics, for example, in his formula linking a magnetic potential within a diamagnetic medium and the magnetic effects of current systems with the magnetization M:

where 4 is the magnetic susceptibility and uM the magnetic potentiaLS4 Helmholtz used this equation to unite all the possible sources of the electric field.55Consequently, he assumed that induced electromotive forces may be produced by time changes of either the vector potential u due to time-variant current systems or the magnetic potential due to the changing magnetization of matter. He termed the important source for an "electric momentum" within a dielectric medium the "dielectric polarization." Like Faraday's notion of "induction," in Helmholtz's theory "polarization" described the displacement of charges within a dielectric medium. The electric momentum 5 1. See e.g., Ludwig Boltzmann, Vorlesungen iiber Maxn~ellsTheorie der Elektricitat und des Lichtes, 2 vols. (Leipzig: Johann Ambrosius Barth, 1891-93; reprinted Braunschweig, Wiesbaden: Friedrich Vieweg, 1982), 2: 133-40. 52. Jed Z. Buchwald, From Maxwell to Microphysics. Aspects of Electromagnetic Theory in the Last Quarter of the Nineteenth Century (Chicago and London: The University of Chicago Press, 1985), 177-86, esp. 177. 53. "Ueber die Bewegungsgleichungen," 556-57, 572-75, 61 1-29; Woodruff, "Contributions," 303-4; and Buchwald, From Maxn~ellto Microphysics. 178-79. 54. "Ueber die Bewegungsggleichungen." 61 7-1 9. 55. Ibid., 614-20.

Formation of Classical Electrodynamics

391

density due to polarization was proportional to the electrostatic field within the medium:

where x,is the dielectric susceptibility of the medium and 4, the scalar potential related to the total electromotive force in the electrically polarizable medium: E, = -V&. The total electromotive force E,, on the other hand, originates from a superposition of a force EEwhich creates the polarization, and an oppositely directed force E,, which results from the polarization charges produced by the action of E,.s~ Although Helmholtz's and Maxwell's systems of field equations contained suggestive formal relationships and common, empirically testable consequences, there were still marked differences in their underlying physical concepts. According to Buchwald, Maxwell's basic physical concept was the displacement (wherever it originates) in an elastic ether filling all space.57This displacement breaks down continuously in a conductor, which causes an ordinary conduction current, and, in turn, produces heat. In vacua and in dielectric media the elastic displacement may remain more stable. Moreover, due to different decay rates of the state of displacement in different media, Maxwell's displacement takes on different values in different media, and, consequently, the divergence of the displacement field may not vanish at the boundary of different media. Maxwell interpreted precisely this nonvanishing divergence of the displacement field as the electric charge. Hence, in Maxwell's electrodynamics (unlike in Continental theories) charge was not an entity in its own physical right but rather a derivative quantity.58 Thus in Maxwell's theory a current did not arise primarily from moving charges or from a flow of charged particles but rather from a time change of displacement. Together with the other differential equations of Maxwell's theory, especially the induction law, Maxwell's extension of Ampcre's law by a displacement current (along with the requirements VB = 0, j = p = 0 in unbounded, nonconducting media) gave rise to wave equations, the solutions to which led to the prediction of transverse electromagnetic waves propagating in the ether. 56. Ibid., 612; and Buchwald, From Maxwell to Microphysics, 179. 57. Buchwald, From Maxwell to Microphysics, 20-40. 58. Ibid., 28; Maxwell, "On Physical Lines of Force," in Niven, ed., Scientific Papers 1:451-5 13, on 491; and idem, "On a Method of Making a Direct Comparison of Electrostatic with Electromagnetic Force," (18681, in Niven, ed., Scientific Paper.7 2: 125-43, on 139.

392

Physicist

Helmholtz, by contrast, did not think primarily let alone exclusively in terms of fields. Instead, like a good Continental theorist he began with moving charges as an ordinary current in a conductor; these current elements act upon one another instantaneously at a distance. However, in responding to Maxwell's theory, Helmholtz concentrated in his theory of polarization on the local reaction of dielectric matter (and, as a tentative extrapolation, of the ether) upon electrical forces, in the sense that in the particles of dielectric matter and in the particles of a dielectric ether (in an otherwise empty space) opposite charges are separated. He called this separation of charges in the particles of a dielectric the "separation of the electricities" ("Scheidung der Elektricitaten") or "dielectric polarization" or, in abbreviated form, the "distrib~tion."~~ Hence the original electromotive forces, which act at a distance, are altered by a contiguously acting state of polarization within a dielectric. In Helmholtz's theory this polarization gave rise to polarization charges which, together with ordinary conduction charges, represented Helmholtz's so-called free charges. First, this density of free charges was subject to the formulation of a continuity equation for charge and current that linked the time change of charges and the (spatial) divergence of a current.60The more important consequence of the dominant role of polarization in Helmholtz's theory was that, unlike in Maxwell's theory of a general time-variant displacement, the current density in Helmholtz's theory was a sum of an ordinary conduction current and a nonconducting term originating from the time change of polarization

ap --A'

at

Finally, central to understanding the different physical concepts used by Maxwell and Helmholtz as the basis for their electrodynamic theories are the different meanings attached to "polarization" and "total electrical field" within a dielectric medium. In Helmholtz's theory of polarization the field of electromotive forces within the dielectric contained not only electrostatic fields, originating from a superposition of an original field and the field of the polarization charges, but also . ~Maxwell's ~ theory, electric fields due to electromagnetic i n d ~ c t i o nIn by contrast, the field of electromotive forces ("electromotive intensi-

59. 60. 61. 62.

"Ueber die Bewegungsgleichungen," 612. Ibid., 611-16. Ibid., 616. Ibid., 572-73, 6 12; and Buchwald, Frorn Maxwell to Microph.vsics, 179-8 1.

Formation of Classical Electrodynamics

393

tiesV)63may create a field of "electric displacement." The latter is subject to variation within dielectric matter due to the varying influence of such matter on the mechanically conceived state of displacement. Thus, the nonconducting part of the current in Maxwell's theory is l a solely the displacement current --D, whereas in Helmholtz's theory c at

Still, an important result of Helmholtz's field theory, which, like the basic interaction potential of currents, was designed to create a greater variety of experimentally testable predictions, was the derivation of the wave equations. Here Helmholtz still concentrated on the standard quantities of a dielectric and diamagnetic medium, namely, polarization and magnetization. He started with a differential equation for the polarization which summed up all the electrodynamic and electrostatic forces polarizing a medium:

Combining his new expression for polarizable media with that for magnetizable media (see p. 390), and thus uncoupling his field equations, Helmholtz anived at two separate wave equations for P and M in a homogenous dielectric and diamagnetic medium:h5

and

Thus Helmholtz's electromagnetic field theory predicted the occurrence of transverse waves of polarization and magnetization propagating in polarizable and magnetizable media. Unlike Maxwell's differential equations with their single solution for transverse waves, Helmholtz's theory also indicated the existence

63. James Clerk Maxwell, A Treatlse on Electricity and Magnetism, 3rd ed., 2 vols. (Oxford: Clarendon Press, 1891; reprinted New York: Dover. 1954), 2252-53 (4 608-1 1). 64. Buchwald, From Maxwell to Microph.vsics, 18 1. 65. "Ueber die Bewegungsgleichungen," 556-58, 6 14-1 5, 6 19, 625-26.

394

Physicist

of longitudinal waves of electric polarization. Referring to the known solutions of the analogue wave equations for the propagation of mechanical perturbations in an elastic solid, Helmholtz concluded that the perturbations of polarization in a dielectric matter travel with different velocities for transversal (v,) and longitudinal (v,) waves:

However, in order to present Maxwell's theory as a limiting case of his own theory, Helmholtz, by simply equating the notorious factor k to 0, allowed the longitudinal waves to disappear. For the case of k = 0 the velocity of the longitudinal waves becomes infinite. In order to formally reconcile the wave equations of Maxwell's theory of light with his own wave equations, Helmholtz further assumed a highly polarizable matter in air and a highly polarizable ether ("Lichtather") in empty space (" Weltraum") (x,and Q equal to infinity in the Maxwellian limit). However, this polarization in turn inevitably tended to compensate the electromotive force engendering the polarization charges. Thus, in effect, Helmholtz's polarization model tended to lose its physical consistency. In 1892, Hertz complained how in Helmholtz's theory for the Maxwellian limit the electrostatic forces acting at a distance almost disappeared completely. Yet Hertz offered no other consolation for a Helmholtzian theorist than to face the inconsistency of, on the one hand, forces acting at a distance and engendering polarization, and, on the other, polarization compensating these forces.66 As already suggested, Helmholtz's measurements of the propagation of nerve impulses almost certainly made him keenly aware of the necessity of general concepts of propagation in time. More specifically, he sought to clarify the validity of the different approaches in electrodynamics, namely, Weber's instantaneous action at a distance of moving charges, Carl Neumann's potentials propagating in time, and Maxwell's theory of contiguous action with its consequence of electromagnetic waves travelling in the electromagnetic ether. Both Neumann's potential theory and Maxwell's field theory assumed that the velocity of propagation was of the order of magnitude of the 66. Heinrich Hertz, Gesammelte Werke, ed. Philipp Lenard, 3 vols. (Leipzig: Johann Ambrosius Barth, 1894-95), vol. 2: Untersuchungen iiber dieAusbreitungder elektrischen Kraji, 2nd ed. (1894), 25-3 1, esp. 27: and Buchwald, From Maxwell to Microphysics, 190-93.

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velocity of light. Hence, immediately after the publication of his theory of wave propagation in dielectric and diamagnetic media Helmholtz began conducting experimental work on the propagation of perturbations in oscillating electrodynamical systems. Measuring only the time lag of electromagnetic induction effects in induction coils at some distance apart, he obtained the rather disappointing result that the velocity of propagation must be greater than 314,400 meters per second.67In a letter to his parents in 1887 Hertz noted this meager result of a lower limit of the propagation velocity: Helmholtz's measurements were especially dissatisfying because Hertz's own experimental results suggested a velocity exceeding even that of light.6*

5. Experimental Tests of Maxwell's Theory: Boltzmann, Hertz, and Helmholtz Helmholtz contributed to the reception of Maxwell's theory not only by noting its intellectual strength, praising its elegant equations, and suggesting experiments in its favor. With his intimate if not unmatched knowledge of both Continental action-at-a-distance theories and Maxwell's contiguous-action theory, Helmholtz was also highly sensitive to the possibilities of either uniting these two theories or reformulating them into a more general theory or demonstrating, through a decisive experiment, the superiority of one theory over the other. One opportunity for so doing emerged in 187 1-72 with the appearance of Boltzmann in Berlin, who came from Vienna to work under Helmholtz in his Berlin physical institute in order to undertake measurements of the specific inductive capacity of insulating substances and so to test the experimental foundations of Maxwell's electromagnetic theory of light. He did so, too, in order partially to balance his education as a purely theoretical physicist by doing some experimental work, while also wanting to come into personal contact with Helmholtz, the prominent holder of the most important chair of physics at a German univ e r ~ i t yAt . ~ first ~ Boltzmann and, ironically, Helmholtz misinterpreted 67. "Ueber die Fortpflanzungsgeschwindigkeit der elektrodynarnischen Wirkungen," MR (1871):292-98, in WA 1:629-35, on 635. 68. Hertz to his parents, 23 December 1887 and 1 January 1888, in Erinnerungen. Briefe, Ihgebiicher. ed. Johanna Hertz (Leipzig: Akademische Verlagsgesellschaft, 1927), 183-86. 69. Boltzmann to Josef Stefan (?). 2 February 1872. Staatsbibliothek Preussischer Kulturbesitz, Berlin, Handschriftenabteilung, Slg. Darrnstaedter F 1 e 1871 (3) L. Boltzmann.

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Boltzmann's measurements of the specific inductive capacity as compared with the indices of the refraction of light. They were uncertain about the well-known Maxwellian relation n = &, where n is the index of refraction and E is the specific inductive capacity, which is related to the dielectric susceptibility according to E = ~ - 4 = n EE~ 47tLE, E = 1 4 n ~ Because . they assumed n = E, Boltzmann at first thought that he had completely disproved Maxwell's electromagnetic theory of light. In point of fact, Boltzmann's data fit quite nicely into the relation n = &.70 Experimental proofs sometimes depend on lucky circumstances; that was certainly the case with Boltzmann's measurements of specific inductive capacity. For Boltzmann mostly measured the specific inductive capacity of nonpolar (for example, organic) substances, where Maxwell's relation indeed holds. Had he measured polar substances (for example, water molecules with their high dipole moment which yield a high inductive capacity), he would have been confronted by numerous deviations from Maxwell's law, deviations that show values of the specific inductive capacity far from n2, which is of the order of magnitude of 1. Although Boltzmann then found impressive experimenta: evidence for Maxwell's electromagnetic theory of light, the latent experimental problems of polar substances, of the dispersion of light in general, and of metal optics showed clear indications of the shortcomings of Maxwell's electrodynamics, which assumed both the ether and matter to be purely continuous and which treated both the specific inductive capacity and the specific resistance as independent of the frequency of the electromagnetic oscillations of light. With the completion of his experimental work, Boltzmann left Berlin and returned to Vienna in 1872. His place in Helmholtz's institute was (in effect) taken up in the late 1870s and early 1880s by Hertz. In a prize question for the Prussian Akademie der Wissenschaften for the year 1879, Helmholtz called for experimental proof of the electrodynamic effect of increasing or diminishing states of polarization in dielectric media." The question reflected the transformation Maxwell's theory of a general displacement current had undergone in Helmholtz's mind. More to the point, Helmholtz's own objective in setting this

+

70. Koenigsberger 2:201; and Walter Kaiser, Introduction, in Boltzmann, Vorlesungen (reprint), on 12*- 13*. 7 1. Adolf Harnack, Geschichte der Koniglichen Preussischen Akademie der Wissenschajien i u Berlin, 3 vols. (Berlin: Reichsdruckerei, 1900), vol. 2: Urkunden und Actenstiicke zur Geschichte der Koniglich Preussischen Akademie der Wissenschajien, 6 17, No. 229.

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question was to stimulate his student Hertz to work on experimentally testing the basic hypotheses of Maxwell's electrodynamics. As Helmholtz solemnly put it in the preface to Hertz's posthumously published Die Prinzipien der Mechanik, he felt from the very beginning of their relationship that in Hertz he had his most promising pupil and one who might promulgate his own scientific ideax7*Nevertheless, for a number of years Hertz sensed a marked reserve in Helmholtz's behavior. Helmholtz did not interfere in the development of Hertz's early scientific career, for example, in Hertz's plan to habilitate at the University of Kiel; indeed, he did all he could to help Hertz. Yet only when Helmholtz received Hertz's first promising paper on the propagation of electrodynamic action under the influence of isolating substances did Helmholtz's tone of voice become truly friendly.73 The objective of a direct experimental test of Maxwell's basic assumption of a displacement current had already been discussed by Maxwell himself.74 Experiments had been undertaken by Nikolai Schiller in 1875 and, especially, by Henry A. Rowland, who worked upon his own proposal in Helmholtz's institute in 1876. Thanks to Helmholtz, Rowland's measurements of (small) magnetic effects of polarization charges moving at high speeds with rotating disks were published in 1876. Contrary to Helmholtz's expectations, however, the results were not decisive. Helmholtz conceded that the effect could either be interpreted within the framework of Weber's theory (as a magnetic effect of moving charges attached to ponderable masses) or in the sense of Maxwell's theory of displacement current or in the sense of his own theory of polarization currents. In the last case, Helmholtz considered the magnetic effect of time-varying polarization as due to air vortices engendered by the rotating disks.75 Hertz's work shows a clear indication of the lasting influence of Helmholtz's prize question of 1879: for example, as already noted, Hertz himself had tried to measure the influence of a massive dielectric attached to the emitting dipole on the propagation of electromagnetic 72. Preface by Helmholtz to Heinrich Hertz, Werke, vol. 3: Die Prinzipien der Mechanik, 2nd ed. (Leipzig: Johann Ambrosius Barth, 1910), xiii-xxviii, on xiv-xvi; and vol. 2: Hertz, Untersuchungen uber die Aushreitung der elektrischen KraF (Leipzig: Johann Ambrosius Barth, 1894), 1 . 73. Hertz to his father, 1 March 1883. in J . Hertz, ed., Erinnerungen, 135-37; Helmholtz to Hertz (postcard), 7 November 1887, in ibid., 180. 74. Salvo d'Agostino, "Hertz's Researches on Electromagnetic Waves," IfSPS 6 (1975):261-323, on 271. 75. "Bericht betreffend Versuche iiber die elektromagnetische Wirkung elektrischer Convection, ausgefiuhrt von Hrn. Henry A.Rowland," AP 158 (1876):487-93, in W 1:791-97, on 796-97.

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action. Moreover, referring to Wilhelm Conrad Rontgen's experiments on the magnetic effect of time-varying states of polarization in a dielectric, Hertz himself was very clear about the relationship of the prize question, of the Rowland and Rontgen experiments, and of his own intermediate experiments in 1887. Here Hertz concentrated on the alleged effect of polarizable dielectric masses on the propagation of electromagnetic action of high frequency. Although this propagation was still not identified as wave propagation, it is hardly surprising that Helmholtz acknowledged the receipt of Hertz's manuscript, which he helped prepare for publication in the Sitzungsberichte of the Prussian Akademie, with an enthusiastic " B r a ~ o ! ! " ~ ~ Notwithstanding the remaining problem of a direct experimental confirmation, Hertz and Helmholtz believed that Hertz's electromagnetic waves meant the scientific breakthrough of Maxwell's theory and its consequent transverse waves. In the introduction to his Untersuchungen iiber die Ausbreitung der elektrischen Kraft, Hertz claimed that the "aim of his experiments was the test of the fundamental hypotheses of the Faraday-Maxwell theory and that the result of the experiments was the confirmation of the fundamental hypotheses of this theory." Historical evidence for this statement can be found as early as 1884 in his theoretical studies on the competing theories, where Hertz concentrated on Maxwell's electrodynamics. Although Hertz avoided the field approach in 1884, instead using formally retarded potentials to derive Maxwell's equation, he in fact already favored Maxwell's theory. And although his derivation was hardly a logically consistent one, for the first time Hertz's paper of 1884 showed the highly symmetrical form of Maxwell's equation in vacuum.77 Like Maxwell's idea of a primarily existing state of displacement in the ether, Hertz stated that the field of electromotive force "is an entity which does exist autonomously in space and which does exist independently from the means of its creation."78 Hence Hertz's later remarks, where he politely praised the influence of his teacher Helmholtz, are best understood as a general indication 76. H. Hertz, "Ueber Inductionserscheinungen, hervorgerufen durch die elektrischen Vorgange in Isolatoren," [I 8871, in Hertz, Untersuchungen, 102-14, esp. 108-1 3; Hertz to Helmholtz, 5 November 1887, in J. Hertz, ed., Erinnerungen, 179-80; and Helmholtz to Hertz, 7 November 1887. 77. D'Agostino, "Hertz's Researches," 284-96; and Kaiser, Theorien der Elektrodynamik, 164-75. 78. H . Hertz, " ~ b e rdie Beziehungen zwischen den Maxwell'schen elektrodynamischen Grundgleichungen und den Grundgleichungen der gegnerischen Elektrodynamik," [1884], in Werke, vol. I: Schrijien vermischten Inhalts (Leipzig: Johann Ambrosius Barth. 1895), 295-314, esp. 296.

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of the stimulating scientific atmosphere in Helmholtz's Berlin institute and of Hertz's general gratitude towards Helmholtz. The closest contact between Helmholtz's theory of dielectric polarization and Hertz's own thinking can be seen in Hertz's previously mentioned intermediate experiments of 1887 aimed at detecting an influence of polarizable matter on the propagation of high-frequency electrodynamic action. Hertz even apologized for not having mentioned Helmholtz in his papers on electromagnetic waves.79 The years from 1886 to 1888 witnessed the triumph, at least in Germany, of Maxwell's electrodynamics: Hertz discharged electricity over a spark gap and thereby found a method for producing and detecting free electromagnetic waves. As discussed above, one typical Hertzian move was to measure the influence of a dielectric in the vicinity of the radiating dipole on the propagation of electromagnetic action.80 Most physicists eventually interpreted Hertz's experiments on electromagnetic waves as the definitive confirmation of Maxwell's prediction of wave solutions for his system of field equations. In particular, Hertz's results on quasi-optical experiments, namely, the reflection, polarization, and interference of electromagnetic waves, were so striking that Hertz, in a lecture before the sixty-second Versammlung deutscher Naturforscher und ~ r z t in e 1889 at Heidelberg, could speak of having almost united the fields of electricity and of light.8' As he later stated: "The aim of these experiments was to confirm the basic hypotheses of Maxwell's theory, and the outcome of these experiments was a confirmation of the basic hypotheses of Maxwell's theory."82 Oliver Heaviside wrote that the discovery of electromagnetic waves was the "death blow" to the old theories of action at a distan~e.~' Nonetheless, despite his final experimental successes, Hertz's research on electromagnetic waves did not confront the basic assumptions of Maxwell's (or Helmholtz's) theory, namely, to show the displacement (or polarization) current directly by experiment. Hertz found an experimental device to test the wave solutions, which Maxwell and Helmholtz could derive from their fundamental field equations. In December 1888 Helmholtz wrote Hertz how "happy" he was about his erstwhile student's latest achievements ("Thaten")-he was 79. Hertz to Helmholtz, 24 February 1892, in J. Hertz, ed., Erinnerungen, 240-41. 80. D'Agostino, "Hertz's Researches," 301. 81. Heinrich Hertz, "Ueber die Beziehung zwischen Licht und Elektricitat" (1889), in his Schriften, 339-54, on 352-53. 82. Hertz, Untersuchungen, 2 1 . 83. Heaviside to Hertz, 13 July 1889, reprinted in O'Hara and Pricha. Hertz and the Maxwellians, 66-8. on 67.

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apparently refening to Hertz's quasi-optical experiments. Yet Helmholtz's letter also betrayed an undertone of self-disappointment: "These are matters that I gnawed around at for years, looking for an opening whereby one could get at them. . . ."84 There is no little irony in the fact that Hertz's principal experimental achievement-the production and detection of polarizable, transverse electromagnetic waves-favored the predictions of Maxwell's theory and questioned the predictive capacity of Helmholtz's theory of dielectric polarization. And it was Hertz, too, who renounced Helmholtz's idea of a modified theory of action at a distance. Accordingly, Helmholtz, in his evaluation of Hertz's experimental work, referred solely to Faraday and Maxwell as the builders of the theoretical basis of Hertz's experiments on electromagnetic waves.85 In his last years Helmholtz again tackled a basic problem in physics which, like the invariance principles, belongs to the metatheoretical level. He ventured to apply the principle of least action to the equations of electrodynamics. This last piece of work in electrodynamics was an attempt to transfer the structural principles of rational mechanics to Maxwell's dynamics of the electromagnetic field. In Bernhard Riemann's and others' theories of action at a distance the derivation of force laws from Lagrangians (representing all the energies of systems of currents or moving charges) was already a well-known theoretical method.86 Maxwell, by contrast, had treated current systems with the help of the principle of least action, using formally electric currents as generalized coordinate^.^' Helmholtz, however, wanted to find a Lagrangian from which one could derive Maxwell's differential equations of the electromagnetic field. Put the other way around, he wanted to unite the entire set of Maxwell's fundamental differential equations into one single equation governed by the principle of least action. Helmholtz's expression for a Lagrangian of the electromagnetic field included electrostatic energy. But more significant was his attempt to propose a so-called kinetic potential, one which still contained polarization and magnetization along with their time variation^.^^ In the hands of Boltzmann, Hendrik Antoon Lorentz, Karl Schwarzschild,

84. Helmholtz to Hertz, 15 December 1888, copy in Deutsches Museum, Munich, Handschriftenabteilung, No. 3 1 10. 85. Helmholtz's preface to Hertz, Die Prinzipien der Mechanik, xx-xxiv. 86. Bernhard Riemann, Schwere, Elektricitat und Magnetismus, Nach den Vorlesungen von Bernhard Riemann vom Sommersemester 1861, ed. Karl Hattendorff (Hannover: Carl Riimpler, 1876), 3 16- 18, 323-27. 87. Maxwell, Treatise 2:223-28 (§ 578-84). 88. "Das Princip der kleinsten Wirkung in der Elektrodynamik," AP 47 (1892):l26. in lt{4 3:476-504, on 485-90.

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and Gustav Mie, this approach became a powerful tool for an elegant representation of field equations in electrodynamics and in the theory of r e l a t i ~ i t y . ~ ~

6. Conclusion Helmholtz's substantive results in electrodynamics were far less successful than either Maxwell's theory of the electromagnetic field or Hertz's experimental confirmation and theoretical clarification of Maxwell's theory or Lorentz's synthesis of particles and fields in his electron theory.y0Helmholtz's importance in shaping classical electrodynamics lay more in stimulating others than in creating his own theory; more in attracting them to his institute and providing them with experimental means than in conducting experiments himselt more in mediating and criticizing than in determining. In short, his role in the formation of classical electrodynamics was an instrumental one. As such, he helped synthesize "classical" physics. Yet at the same time his electrodynamics, even as it became increasingly obsolete after 1890, contained elements that others would pursue to help shape "modern" physics. For one, his polarization theory, with its consequence of longitudinal waves, was used as a theoretical basis in experimental areas beyond dielectric media. In particular, cathode rays were interpreted as longitudinal waves. Helmholtz himself was inclined to think of these rays as longitudinal waves in the And again in 1895, barely a year after Helmholtz's death, when Rontgen found a new type of radiation, the X-rays, the longitudinal ether waves appeared: in his preliminary announcement to the Physikalisch-Medicinische Gesellschaft in Wiirzburg Rontgen suggested interpreting his discovery as experimental proof of the predicted longitudinal undulations in the ether.y2For another, Helmholtz's work in electrodynamics contained vague ideas foreshadowing relativity: for 89. See, e.g., Wolfgang Pauli, "Raelitivitatstheorie," in Encyklopadie der mathematischen Wissenschatien. Mil Einschluss ihrer Anwendungen, eds., H. Burkhardt, et al., 6 vols. in several parts (Leipzig: B.G. Teubner, 1896-1935), 5:2: Physik, ed. Arnold Sommerfeld (1920), 539-775, on 642-43, 755; and Gunter Bierhalter's essay, "Helmholtz's Mechanical Foundation of Thermodynamics," in this volume. 90. Hendrik Antoon Lorentz, "La thCorie ClectromagnCtique de Maxwell et son application aux corps mouvants," archive.^ ni.erlandaises des sciences e.vactes et naturelles 25. str. 1 (1892):363-552. on 475-97. For Helmholtz's influence on Lorentz see Ole Knudsen. "Electric Displacement and the Development of Optics after Maxwell," C'entaurus 22 ( 1978):53-60. 9 1 . Koenigsberger 2:305. 92. Wilhelm Conrad Rontgen, "Ueber eine neue Art von Strahlen," Sitzungsberichte der ph~!~ikaIisc11-tnedic~nischcn Ges~llschafiin W'urzhurg 137 ( 1 895):132-41. on 140-4 1.

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example, in his tentative introduction of retardation effects in his basic law for electrodynamic interaction. Along with the contemporary work of Riemann, Enrico Betti, Ludvig Valentin Lorenz, and Tullio LeviCivita on retarded potentials, which took into account the finite velocity of propagation of electromagnetic action, the overall thrust of Helmholtz's electrodynamics clearly constituted within the electrodynamic arena the continuing erosion of the Newtonian physical world vie^.^^ Whether or not Helmholtz's generalized vector potential for the interaction of distant current elements was a conscious abandonment of the structures of classical mechanics, it nonetheless shattered the predominant position of electrodynamic theories like Weber's. Ideas foreshadowing relativity can also be seen in Helmholtz's attempt to find an appropriate Lagrangian for the electromagnetic field, and, though this did not appear directly in his electrodynamics, in his stress on the empirical character of the axioms of geometry.94 Yet even as he helped point the way to the future, Helmholtz remained firmly rooted in nineteenth-century traditions. With his criticism of theories of action at a distance, with his formulation of a generalized potential for the fundamental electrodynamic interaction, and with his own generalized field equations he stimulated the reception and eventual establishment of Maxwellian electrodynamics. Together with his work on hydrodynamics and on thermodynamics, his electrodynamics greatly influenced the formation of classical theoretical physics as a whole. Yet unlike his British colleagues and unlike Boltzmann, Helmholtz always remained very cautious with hypotheses concerning the microphysical level. In that respect, at least, his work accurately reflected the epistemological atmosphere in physics in the German-speaking countries during the second half of the nineteenth century.

93. Treder, "Helmholtzsche Elektrodynamik"; idem, "Helmholtzsche Elektrodynamik und die Beziehungen von knematik"; W. Kaiser, "Die zeitliche Ausbreitung von Potentialen in der Elektrodynamik," Gesnerus 35 (1978):279-317; Wiechert, "Grundlagen," 78-9; and Tullio Levi-Civita, "Sulla reductibiliti delle equazioni elettrodinamiche di Helmholtz alla forma Hertziana," I1 Nuovo Cimento, 6th ser. (1897):93-108. 94. On this last point see Robert DiSalle's essay, "Helmholtz's Empiricist Philosophy of Mathematics: Between Laws of Perception and Laws of Nature," in this volume.

Between Physics and Chemistry Helmholtz's Route to a Theory of Chemical Thermodynamics Helge Kragh

1. Introduction Mid-nineteenth-century chemistry was almost a purely experimental and classificatory science. In contrast to physics, it largely lacked theoretical foundations and showed little progress in supplying such foundations. Nearly all chemists merely collected data and analyzed specific compounds-an empiricist trend reinforced by the emergence in the 1830s of the powerful new subdiscipline of organic chemistry. In 1873, the distinguished chemist and historian of chemistry, Hermann Kopp, confessed that in "chemistry, no theory has yet been developed which attempts to derive the results of experience as necessary consequences of a definite principle. The theoretical principles of chemistry are still only applicable to more or less special cases in practical chemistry. As yet we have no comprehensive picture of the connections between these special cases or of the image which we construct from them, however we imagine these connections."l Most chemists agreed. Nonetheless, some progress had been made, particularly in the fields of chemical equilibrium and rates of reaction, electrochemistry, and thermochemistry.2 The theoretical foundation for much of this work Acknowledgments: I would like to thank Pat Munday for comments on this paper, and David Cahan for extensive criticism and many helpful suggestions. 1. Hermann Kopp, Die Entwicklung der Chemie in der nczceren Zeit (Munich: R. Oldenburg, 1873), 844. 2. For brief descriptions of these developments, see, e.g., Aaron J. Ihde, The Development of Modern Clhemrstry (New York: Dover, 1984), 39 1-41 7; and A.J.B. Rob-

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was the concept of "chemical force," or "affinity," the nature of which was, however, obscure. It was at first widely assumed that the affinity of chemical substances would find its explanation in terms of gravitational or electrical forces, or perhaps by means of mechanical models of molecules; yet nothing came of these speculations. Then with the establishment of the principle of energy conservation around 1850 the heat evolved in chemical processes seemed to offer a quantitative measure of affinity and so to provide a theoretical basis for chemical change. Chemists applied the thermal theory of affinity to chemical reactions and used it to study chemical equilibria and electrochemical processes. For these processes it was generally assumed that the electrical heat produced by the electromotive force of the cell equalled the chemical heat, in which case electrochemistry could presumedly be understood in terms of thermochemistry. According to classical thermochemistry, as founded by Julius Thomsen and Marcellin Berthelot, the heat evolved in a chemical reaction was the true measure of its a f f i n i t ~The . ~ theory rested on the Thomsen-Berthelot principle that all chemical changes were accompanied by heat production and that the actual process which occurred was the one in which the most heat was produced. This principle, formulated in slightly different versions by Thomsen in 1854 and by Berthelot in 1864, became the controversial foundation of a research program that lasted for two decades. It was criticized from the start on theoretical and empirical grounds; by 1880, it was widely recognized that the thermal theory of affinity needed replacement. Its successor, as physicists more than chemists recognized, would have to rely on the second law of thermodynamics. Although this law, along with the associated concept of entropy, had been introduced in the 1850s (by Rudolf Clausius, William Thomson [Lord Kelvin], William Rankine, and others), it had diffused only slowly to chemistry. The new theory, as it emerged during the 1880s, transformed the methodology of theoretical chemistry without constituting a revolutionary break with its past. The traditional conceptual objects of chemistry were atoms and molecules; yet many chemists argued that such objects served only a heuristic purpose and had no real existence. Positivistically oriented

ertson, "Physical Chemistry," in Colin A. Russell, ed., Recent Developments in the History of Chemistry (London: The Royal Society of Chemistry. 1985), 153-78. 3. For this theory and references to the literature, see Helge Kragh, "Julius Thornsen and Classical Thermochemistry," BJHS 1 7 (1984):255-72; and R.G.A. Dolby, "Therrnochemistry versus Thermodynamics: The Nineteenth-century Controversy," Htstorv of Sc~ence22 ( 1984):375-400.

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chemists maintained that a realistic interpretation of atoms and molecules was "metaphysical" and that chemistry should build solely on measurable quantities, such as equivalent weight^.^ Such philosophical niceties notwithstanding, in practice much of chemistry was firmly based on the assumption of atoms and molecules. Yet during the latter part of the century many chemists and physicists thought that this assumption blocked the path to a proper theoretical understanding of chemical phenomena; Berthelot, Josiah Willard Gibbs, Pierre Duhem, Wilhelm Ostwald, and Georg Helm, among others, assumed a general theory would be neutral with respect to hypotheses about the constitution of matter, and they regarded hydro- and thermodynamics as methodological models for future chemical theory. The transformation of chemistry from a largely static and experimental into a dynamic and theoretical science was produced not by run-of-the-mill chemists but by physicists or chemists with a strong background in physics. Hermann von Helmholtz was one such important figure in that transformation; others were Gibbs, Ostwald, August Horstmann, Svante Arrhenius, and Jacobus Henricus van't HoK Although Helmholtz was not a chemist, his contributions to the fields of electrochemistry and chemical thermodynamics secured him a distinguished place in the history of ~ h e m i s t r y That . ~ reputation rested, above all, on his thermodynamic explanation (in 1882) of chemical changes, an explanation that provided chemistry with a solid theoretical foundation. Building on earlier insights gained by himself and other scientists, Helmholtz proved that affinity was not given by the heat evolved in a chemical reaction but rather by the maximum work produced when the reaction was carried out reversibly. Characteristically, Helmholtz's demonstration was the result of abstract physical reasoning and not of chemical experimentation. His work of 1882-83 was convincing evidence that advanced physical theory had a fruitful role to play even in the traditionally empirical science of chemistry. Although organic chemists continued to distrust the increasing mathematization of chemistry, by 1890 theoretical chemistry had undeniably evolved into an important and useful subdiscipline. Helmholtz

4. See David M. Knight, Atoms and Elements (London: Hutchison, 1967); and Helge Kragh, "Julius Thomsen and 19th-Century Speculations on the Complexity of Atoms." Annals of Science 39 (1982):37-60. 5. For appreciations of Helmholtz's work in chemistry, see Wilhelm Ostwald, GroJe Manner (Leipzig: Akademische Verlagsgesellschaft, 1909), 265-3 1 1 ; Walther Nernst, "Die elektrochemischen Arbeiten von Helmholtz," D1e NaturwissenschaJen 9 (1921):699-702; and Karl Heinig, "Einige Bemerkungen zu Helmholtz's wissenschaftlichem Wirken und der Chemie des 19. Jahrhunderts." WZHUB 22 (1973):357-61. See also the references to Section 4 of the present essay, especially notes 68-81.

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was neither the sole nor the most important contributor to this development; but his thermodynamic theory of 1882-83 was the pioneering work on which much of the new theoretical chemistry rested. Helmholtz's route to chemical thermodynamics was long and tortuous; it was only after many years' occupation with energetics6 and electrochemistry-disrupted by a long period of work in physiologythat he realized how to incorporate fully the laws of thermodynamics into chemistry. For Helmholtz, as for nineteenth-century science in general, energetics, thermodynamics, and electrochemistry were inseparably bound. In order to understand his chemical thermodynamics, and thereby to appreciate better the methodological transformation of chemistry in the late nineteenth century, this essay first examines his earlier work in electrochemistry and related areas. This is the subject of Section 2, which surveys Helmholtz's early work in physiological chemistry (1843-45), the chemical parts of his 1847 treatise on energy conservation, his work on galvanic polarization and concentration cells (1872-77), and, finally, his analysis of the atomic nature of electricity (1880-81). Apart from their importance as prologue to Helmholtz's theory of 1882, these contributions also had considerable importance in their own right and were widely appreciated by contemporary chemists. In his theory of chemical thermodynamics, the subject of Section 3 below, Helmholtz introduced the fundamental concept of free energy; he thereby eliminated the old thermal notion of affinity. His work of 1882-83 proved important for the new field of physical chemistry which emerged a few years later. Yet Helmholtz's support of the physical chemistry of Ostwald, van't Hoff, and Arrhenius was not wholehearted; indeed, he was skeptical of the ionic theory of dissociation, a cornerstone of the new theory. Section 4 examines the relation of Helmholtz's work in chemical thermodynamics to the new physical chemistry and evaluates the influence of Helmholtz's work on chemistry as a whole.

2. Energetics and Electrochemistry Helmholtz's initiation into the sciences of his day included a solid education in chemistry. As a medical student at Berlin's Koniglich medizinisch-chirurgisches Friedrich-Wilhelms-Institut, he attended Eilhard Mitscherlich's lectures on chemistry; yet he apparently found 6. Here and elsewhere in this essay, "energetics" refers to the science of energy and its transformations, and not to the viewpoint developed in the 1890s by the energeticist school of Ostwald, Helm. and others.

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the lectures boring and the laboratory exercises tedious.' He passed his preliminary examinations in December 1839 and received his high. ~ was apparently not inest mark ("vorzuglich gut") in ~ h e m i s t r y He terested in chemistry for its own sake, yet he realized that it would be useful to him for his work in physics and physiology. Decades later, in the course of giving advice to his son Robert, Helmholtz revealed his own attitude towards chemistry: "Chemistry can really interest only those who, in order to gain firsthand experience of the circumstances, have themselves made experiments in it . . . . After all, a certain amount of chemical knowledge is essential for progress in the (other)

science^."^ It was the physiological aspects of chemistry that interested the young Helmholtz. His first publications dealt with physiological chemistry and animal heat, a fact that reflected, on the one hand, the influence of Justus von Liebig-Helmholtz rather sardonically (and prion the other, the vately) anointed him "the king of chemist~"~~-and, tension between physiology and chemistry in explaining organic processes. In his very first publication (1843), Helmholtz confirmed the observation of Theodor Schwann and others of the vegetable nature of yeast. Most chemists, according to Helmholtz, considered this controversial conclusion to be based on "physiologcal phantasies."ll The burning issue of the day in chemistry and physiology was that of "vitalism" versus "mechanism." The vitalists believed that processes in organic nature were governed not only by the general laws of physics 7. David Cahan, ed., Letters ofHermann von Helmholtz to His Parents: The Medical Education of a German Scientist, 1837-1846 (Stuttgart: Franz Steiner Verlag, 1993), Letter 6 (5 November 1838), Letter 9 (5 May 1839), and Letter 12 (1 1 July 1839). 4852. 56-60, 65-6, resp. 8. Ibid., Letter 16 (1 1 December 1839), 74-5. In physics. psychology, zoology, and botany, Helmholtz received a "sehr gut," and in mineralogy a "ziemlich gut." (Ibid.) 9. Hermann von Helmholtz to Robert von Helmholtz, 4 July 1880, in Ellen von Siemens-Helmholtz, ed., Anna von Helmholtz. Ein Lebensbild in Briefen, 2 vols. (Berlin: Vcrlag fiir Kulturpolitik, 1929). 1:248-50, quote o n 249. Helmholtz advised Robert to attend a course in inorganic chemical analysis in Robert Bunsen's laboratory. (Ibid.) 10. Helmholtz to Olga von Helmholtz, 10 August 1851, in Richard L. Kremer, ed., Letters of Hermann von Helmholtz to His Wife, 1847-1859 (Stuttgart: Franz Steiner, 1990), 53-60, quote on 56. l I. "Ueber das Wesen der Faulniss und Gahrung," MA (l843):453-62, in WA 2:72634, quote on 727. For the vexing question of "vitalism" in the works of Liebig and Helmholtz, see Yehuda Elkana, The Discovery of the Conservation ofEnergy (London: Hutchison, 1974), 103-1 1; Timothy Lenoir, The Strategy of Life. Teleology and Mechanics in Nineteenth Century German Biology (Dordrecht: Reidel, 1982), 197-21 5; and Richard Lynn Kremer, "The Thermodynamics of Life and Experimental Physiology, 1770-1 880," (Ph.D. diss., Harvard University, 1984), chap. 6: "Animal Heat and Energy Conservation, 1837-1847." For Helmholtz's early work in physiology see the essay by Kathryn M. Olesko and Frederic L. Holmes, "Experiment, Quantification, and Discovery: Helmholtz's Early Physiological Researches, 1843-50," in this volume.

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and chemistry, but also by the purposeful action of a special "vital force." Extreme mechanists or reductionists, by contrast, argued that biological phenomena could be fully reduced to physical-chemical processes. Although Helmholtz sympathized with Liebig's version of antivitalism, his conclusions gave only ambiguous support to "the greatest of living chemists,"12 as he called Liebig. Helmholtz showed experimentally that putrefaction and fermentation could not be due to either very hot air or electrolytic oxygen, which led him to conclude, with Liebig, that putrefaction could be maintained independently of vital processes. But he also argued, against Liebig, that fermentation was essentially a different type of organic process, namely "a form of putrefaction bound to and modified by the presence of an organism."13 Whereas Helmholtz's first paper was not concerned with the problem of the origin and transformation of organic ("animal") heat, his second was.14 In critically reviewing the problem of animal heat as given in Liebig's " ~ b e rdie thierische Warme," he demonstrated a sure knowledge of the still immature science of thermochemistry and discussed various experimental determinations of the heat of combustion of carbon, a topic of evident importance to the problem of animal heat and energy conservation in the organic world. He criticized results-of CCsar Despretz, Pierre Dulong, Pierre Favre, and Johann Silbermann-that were not based on the mechanical theory of heat. That criticism indicated Helmholtz's growing conviction of the unity of natural forces and pointed toward his idea of the conservation of force, published two years later (1847). "In considering heat as motion," he wrote in 1845, "we must first suppose that mechanical, electrical, and chemical forces can produce only a definite equivalent of work, however complicated the manner of transformation of one force into another may be."I5 The chemical content of Helmholtz's epochmaking study of 1847Ueber die Erhaltung der Kraft-included two areas to which Helmholtz would later greatly contribute: thermochemistry and electrochemistry. In Section IV of his study, he dealt with the heat formed by chemical

12. Helmholtz to Olga von Helmholtz, 10 August 1851, on 56. 13. "Faulniss und Gahrung," 437. 14. "Bericht iiber die Theorie der physiologschen Warmeerscheinungen fiir 1845," in Fortschritte der Physik i m Jahre 1845 (Berlin, 1847), 346-55, in WA 1:3-11. 15. Ibid., 1:7. Although Helmholtz here expressed the idea of the unity of forces, he did not articulate it into the principle of energy conservation. (See Thomas S. Kuhn, "Energy Conservation as an Example of Simultaneous Discovery," in Kuhn's The Essential Tension: Selected Studies in Scientific Tradition and Change [Chicago and London: The University of Chicago Press, 19771, 66-104, esp. 95.)

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processes. Referring to Germain Henri Hess's recently stated law that the amount of heat evolved in a chemical process was independent of the steps through which the reaction occurred, Helmholtz argued that this result simply reflected the principle of force conservation. Hess had originally derived his law on the assumption that heat was a substance; Helmholtz showed that this assumption was unnecessary. "According to our way of viewing the subject," he wrote, "the quantity of heat developed by chemical processes would be the quantity of vis viva produced by the chemical attractions, and in this case the above law [Hess's] would be the expression for the principle of the conservation of force."I6 Helmholtz then went on to address the earlier works of Benoit-Pierre-Emile Clapeyron and Karl Holtzmann ( 1 834 and 1845, respectively) which were based on Sadi Carnot's theory of thermal work and the associated caloric notion of heat. Holtzmann and Clapeyron had derived different equations for the conversion coefficient between heat and mechanical force; Helmholtz showed that, when seen from the point of view of conservation of force, these equations were identical. In Section V of Ueber die Erhaltung der Kraft Helmholtz discussed polarization, contact electricity, and various kinds of galvanic cells from the point of view of conservation of force. Using the simple case of a Daniel1 cell or a battery consisting of such cells, he argued that the net (electrical) heat produced arose from the difference in the chemical heats evolved at the two electrodes. Denoting the heat produced by one equivalent of the electropositive metal by its oxidation and dissolution a, and the corresponding heat absorbed at the electronegative metal a,, he found the electromotive force 8 0 f the cell to be given by 8=a,--a,, which implied that the electromotive force was fully reducible to thermochemical quantities. James Prescott Joule had reached a similar conclusion in 1841 using proportionality instead of equality; and William Thomson in 1851 confirmed the equality of chemical and electric heats." This general idea that in a galvanic cell chemical energy was completely transformed into electric energy was subsequently often referred to as the "Thomson-Helmholtz rule." In his 1847 masterpiece, Helmholtz assumed that each kind of matter had a specific affinity for electricity, positive or negative, and that 16. "Ueber die Erhaltung der Kraft. Eine physikalische Abhandlung," U'A 1:12-75, first published in book form (Berlin: G. Reimer, 1847). For an analysis of this work see the essay by Fabio Bevilacqua, "Helmholtz's Creherdie Erhaltung der Krufi: The Emergence of a Theoretical Physicist," in this volume. 17. See Wilhelm Ostwald, Electrochernistrv. History and Theory, 2 vols. (Leipzig: Veit & Co.. 1896: reprinted New Delhi: .American Publishing Co.. 1980), 2:743-66.

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during electrolysis work was done in separating atoms from their electrical charges rather than in dissociating the atoms. He referred repeatedly to "electrical particles" and composite atoms with internal degrees of freedom and imagined that "portions of the composite atom of a liquid are endowed with different powers of attraction for electricities." According to Helmholtz, during electrolysis these portions of atoms were separated on the electrodes to which they deposited their electricity. "We can therefore consider," he wrote, "that in chemical compounds the atoms are also associated with equivalent quantities of electricity + E. These quantities of electricity are just as equal for all atoms as the stoichiometric equivalents of ponderable substances in different compounds."l8 Thus, as early as 1847 Helmholtz considered electricity to be corpuscular in nature, a view which was then far from common. In sum, Helmholtz's early works show that already by 1847 he had a solid understanding of thermochemical and electrochemical matters. He used that understanding to advance his larger scientific program. Despite his early, mid-century achievements in electrochemistry, Helmholtz refrained from further electrochemical studies for a full quarter of a century and instead devoted himself principally to physiological investigations. With his appointment in 1871 as the new professor of experimental physics at the University of Berlin, he devoted all his efforts to physical enquiries. In 1872-73, he resumed his electrochemical studies with an investigation of galvanic polarization in a Daniell element connected to an electrolytic cell with platinum electrodes.19 It was well known that in such a system the "polarizing current" from the Daniell element declined rapidly but without ever entirely vanishing; for small currents no decomposition of water was observed. When the electrolytic system was disconnected, the platinum cell would decompose water and produce a "depolarizing" current that soon became imperceptible. (Helmholtz introduced the terms polarizing and depolarizing currents.) To explain this phenomenon, Helmholtz characteristically focused on its apparent contradiction with the principle of energy conservation (as the conservation of "force" had by then become known). He asked: "On what does the apparently unlimited duration of the polarizing current depend? In a series specified as above (that is, a Daniell element connected to a platinum cell), if no other changes occur in it, then the electrolytic conduction in the 18. "Ueber die Erhaltung der Kraft," WA 1:54. 19. "Ueber die galvanische Polarisation des Platin," Halle, Zeitschrift fur die gesammfen Naturwissenschaften 6 (1872): 186-88; and "Ueber galvanische Polarisation in gasfreien Fliissigkeiten," AP 150 (1873):483-95. in WA 1323-34.

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liquids, as predicted by Faraday's law, cannot come about without violating the law of the conservation of energy."20Helmholtz saw that any explanation had to agree with Faraday's law as well as with the law of energy conservation. He suggested that the platinum cell acted like an imperfect capacitor, an analogy that James Clerk Maxwell had also suggested about this time.21Helmholtz argued that the mechanism occurring in the platinum cell capacitor was what he called an electrolytic convection: in galvanic processes the gases (hydrogen and oxygen) would not necessarily evolve as bubbles, but might instead move within the liquid or penetrate the surface layer of the platinum plates. In this way he explained the puzzling fact that a very small electromotive force could cause a current without water being decomposed. Helmholtz got the idea that hydrogen-and, to a much lesser extent, oxygen-can diffuse into certain metals, a process known as occlusion, from Thomas Graham, who in 1858 had demonstrated the effect for palladium.22 In 1872-73, Helmholtz provided partial experimental support for his suggestion of electrolytic convection currents and the role of occlusion effects in platinum. In 1876, the American physicist Elihu Root, who worked in Helmholtz's laboratory in Berlin, supplied definitive experimental proof of the correctness of Helmholtz's theory.?' By 1873, then, Helmholtz had broadened the spectrum of processes by which electrochemical action could occur. Nonetheless, he still adhered to the thermal notion of affinity, according to which the heat of combustion of hydrogen provided a theoretical limit below which the decomposition of water could not occur. He stated this view explicitly, and it is only from this viewpoint that the case of a Daniel1 cell connected to a platinum electrolytic cell constituted a puzzle in need of explanation: from the viewpoint of the second law of thermodynamics-still not incorporated into chemistry-electrochemical processes that consumed more heat than supplied electrically would not necessarily conflict with the law of conservation of energy.24Although Helmholtz thus based his theory on false premises-the thermal theory

20. "Ueber gasfreien Flussigkeiten," W:4 1:824. 2 1. James Clerk Maxwell, .4 Treatise on Electricity and Magnetism, 2 vols. (Oxford: Clarendon Press, 1873), 1:322. 22. Thomas Graham, "On the Occlusion of Hydrogen Gas by Metals," Proceed;ngs o f the Royal Societj, 16 ( 1 868):422-27. 23. Elihu Root, "Versuche iiber die Durchdringung des Platina mit elektrolytischen Gasen." ME (1876):217-20. See also Helmholtz's "Bericht uber Versuche des Hrn. Dr. E. Root aus Boston, die Durchdringung des Platins mit elektrolytischen Gasen betreffend," A P 159 ( 1 876):4 16-20, in 14